# 2. 어휘 분석

A Python program is read by a parser. Input to the parser is a stream of tokens, generated by the lexical analyzer (also known as the tokenizer). This chapter describes how the lexical analyzer produces these tokens.

The lexical analyzer determines the program text’s encoding (UTF-8 by default), and decodes the text into source characters. If the text cannot be decoded, a `SyntaxError` is raised.

Next, the lexical analyzer uses the source characters to generate a stream of tokens. The type of a generated token generally depends on the next source character to be processed. Similarly, other special behavior of the analyzer depends on the first source character that hasn’t yet been processed. The following table gives a quick summary of these source characters, with links to sections that contain more information.

Character | Next token (or other relevant documentation)
--- | ---

- 스페이스

- 탭

- formfeed

- Whitespace

- CR, LF

- New line

- Indentation

- backslash (`\`)

- Explicit line joining

- (Also significant in string escape sequences)

- hash (`#`)

- Comment

- quote (`'`, `"`)

- String literal

- ASCII letter (`a`-`z`, `A`-`Z`)

- non-ASCII character

- Name

- Prefixed string or bytes literal

- underscore (`_`)

- Name

- (Can also be part of numeric literals)

- number (`0`-`9`)

- Numeric literal

- dot (`.`)

- Numeric literal

- Operator

- question mark (`?`)

- dollar (`$`)

- backquote (`​`​`)

- control character

- Error (outside string literals and comments)

- other printing character

- Operator or delimiter

- end of file

- End marker

## 2.1. 줄 구조(Line structure)

파이썬 프로그램은 여러 개의 논리적인 줄(logical lines) 들로 나뉩니다.

### 2.1.1. 논리적인 줄

The end of a logical line is represented by the token `NEWLINE`. Statements cannot cross logical line boundaries except where `NEWLINE` is allowed by the syntax (e.g., between statements in compound statements). A logical line is constructed from one or more physical lines by following the explicit or implicit line joining rules.

### 2.1.2. 물리적인 줄

A physical line is a sequence of characters terminated by one the following end-of-line sequences:

- the Unix form using ASCII LF (linefeed),

- the Windows form using the ASCII sequence CR LF (return followed by linefeed),

- the ‘Classic Mac OS’ form using the ASCII CR (return) character.

Regardless of platform, each of these sequences is replaced by a single ASCII LF (linefeed) character. (This is done even inside string literals.) Each line can use any of the sequences; they do not need to be consistent within a file.

The end of input also serves as an implicit terminator for the final physical line.

Formally:

    newline: <ASCII LF> | <ASCII CR> <ASCII LF> | <ASCII CR>

### 2.1.3. 주석

주석은 문자열 리터럴에 포함되지 않는 해시 문자(`#`)로 시작하고 물리적인 줄의 끝에서 끝납니다. 묵시적인 줄 결합 규칙이 유효하지 않은 이상, 주석은 논리적인 줄을 종료시킵니다. 주석은 문법이 무시합니다.

### 2.1.4. 인코딩 선언

파이썬 스크립트의 첫 번 째나 두 번째 줄에 있는 주석이 정규식 `coding[=:]\s*([-\w.]+)` 과 매치되면, 이 주석은 인코딩 선언으로 처리됩니다. 이 정규식의 첫 번째 그룹은 소스 코드 파일의 인코딩 이름을 지정합니다. 인코딩 선언은 줄 전체에 홀로 나와야 합니다. 만약 두 번째 줄이라면, 첫 번째 줄 역시 주석만 있어야 합니다. 인코딩 선언의 권장 형태는 두 개입니다. 하나는

    # -*- coding: <encoding-name> -*-

인데 GNU Emacs에서도 인식됩니다. 다른 하나는

    # vim:fileencoding=<encoding-name>

인데 Bram Moolenaar 의 VIM에서 인식됩니다.

If no encoding declaration is found, the default encoding is UTF-8. If the implicit or explicit encoding of a file is UTF-8, an initial UTF-8 byte-order mark (`b'\xef\xbb\xbf'`) is ignored rather than being a syntax error.

인코딩이 선언되면, 인코딩 이름은 파이썬이 인식할 수 있어야 합니다 (표준 인코딩를 참조하세요). 인코딩은 문자열 리터럴, 주석, 식별자를 포함한 모든 어휘 분석에서 모두 사용됩니다.

All lexical analysis, including string literals, comments and identifiers, works on Unicode text decoded using the source encoding. Any Unicode code point, except the NUL control character, can appear in Python source.

    source_character:  <any Unicode code point, except NUL>

### 2.1.5. 명시적인 줄 결합

둘 이상의 물리적인 줄은 역 슬래시 문자(`\`)를 사용해서 논리적인 줄로 결합할 수 있습니다: 물리적인 줄이 문자열 리터럴이나 주석의 일부가 아닌 역 슬래시 문자로 끝나면, 역 슬래시와 뒤따르는 개행 문자가 제거된 채로, 현재 만들어지고 있는 논리적인 줄에 합쳐집니다. 예를 들어:

    if 1900 < year < 2100 and 1 <= month <= 12 \
       and 1 <= day <= 31 and 0 <= hour < 24 \
       and 0 <= minute < 60 and 0 <= second < 60:   # 유효한 날짜처럼 보입니다
            return 1

역 슬래시로 끝나는 줄은 주석이 포함될 수 없습니다. 역 슬래시는 주석을 결합하지 못합니다. 역 슬래시는 문자열 리터럴을 제외한 어떤 토큰도 결합하지 못합니다 (즉, 문자열 리터럴 이외의 어떤 토큰도 역 슬래시를 사용해서 두 줄에 나누어 기록할 수 없습니다.). 문자열 리터럴 밖에 있는 역 슬래시가 앞에서 언급한 장소 이외의 곳에 등장하는 것은 문법에 어긋납니다.

### 2.1.6. 묵시적인 줄 결합

괄호(`()`), 대괄호(`[]`), 중괄호(`{}`)가 사용되는 표현은 역 슬래시 없이도 여러 개의 물리적인 줄로 나눌 수 있습니다. 예를 들어:

    month_names = ['Januari', 'Februari', 'Maart',      # 이것들은
                   'April',   'Mei',      'Juni',       # 일년을 이루는
                   'Juli',    'Augustus', 'September',  # 달들의
                   'Oktober', 'November', 'December']   # 네덜란드 이름입니다

묵시적으로 이어지는 줄들은 주석을 포함할 수 있습니다. 이어지는 줄들의 들여쓰기는 중요하지 않습니다. 중간에 빈 줄이 들어가도 됩니다. 묵시적으로 줄 결합하는 줄 들 간에는 NEWLINE 토큰이 만들어지지 않습니다. 묵시적으로 이어지는 줄들은 삼중 따옴표 된 문자열들에서도 등장할 수 있는데 (아래를 보라), 이 경우는 주석이 포함될 수 없습니다.

### 2.1.7. 빈 줄

A logical line that contains only spaces, tabs, formfeeds and possibly a comment, is ignored (i.e., no `NEWLINE` token is generated). During interactive input of statements, handling of a blank line may differ depending on the implementation of the read-eval-print loop. In the standard interactive interpreter, an entirely blank logical line (that is, one containing not even whitespace or a comment) terminates a multi-line statement.

### 2.1.8. 들여쓰기

논리적인 줄의 제일 앞에 오는 공백(스페이스와 탭)은 줄의 들여쓰기 수준을 계산하는 데 사용되고, 이는 다시 문장들의 묶음을 결정하는 데 사용되게 됩니다.

탭은 (왼쪽에서 오른쪽으로) 1~8개의 스페이스로 변환되는데, 치환된 후의 총 스페이스 문자 수가 8의 배수가 되도록 맞춥니다. (유닉스에서 사용되는 규칙에 맞추려는 것입니다.) 첫 번째 비 공백 문자 앞에 나오는 공백의 총수가 줄의 들여쓰기를 결정합니다. 들여쓰기는 역 슬래시를 사용해서 여러 개의 물리적인 줄로 나눠질 수 없습니다; 첫 번째 역 슬래시 이전의 공백이 들여쓰기를 결정합니다.

소스 파일이 탭과 스페이스를 섞어 쓰는 경우, 탭이 몇 개의 스페이스에 해당하는지에 따라 다르게 해석될 수 있으면 `TabError` 를 일으킵니다.

크로스-플랫폼 호환성 유의 사항: UNIX 이외의 플랫폼에서 편집기들이 동작하는 방식 때문에, 하나의 파일 내에서 들여쓰기를 위해 탭과 스페이스를 섞어 쓰는 것은 현명한 선택이 아닙니다. 다른 플랫폼들에서는 최대 들여쓰기 수준에 제한이 있을 수도 있다는 점도 주의해야 합니다.

폼 피드 문자는 줄의 처음에 나올 수 있습니다; 앞서 설명한 들여쓰기 수준 계산에서는 무시됩니다. 선행 공백의 다른 곳에 등장하는 폼 피드 문자는 정의되지 않은 효과를 줍니다 (가령, 스페이스 수가 0으로 초기화될 수 있습니다).

The indentation levels of consecutive lines are used to generate `INDENT` and `DEDENT` tokens, using a stack, as follows.

Before the first line of the file is read, a single zero is pushed on the stack; this will never be popped off again. The numbers pushed on the stack will always be strictly increasing from bottom to top. At the beginning of each logical line, the line’s indentation level is compared to the top of the stack. If it is equal, nothing happens. If it is larger, it is pushed on the stack, and one `INDENT` token is generated. If it is smaller, it must be one of the numbers occurring on the stack; all numbers on the stack that are larger are popped off, and for each number popped off a `DEDENT` token is generated. At the end of the file, a `DEDENT` token is generated for each number remaining on the stack that is larger than zero.

여기에 (혼란스럽다 할지라도) 올바르게 들여쓰기 된 파이썬 코드 조각이 있습니다:

    def perm(l):
            # l 의 모든 순열의 리스트를 계산합니다
        if len(l) <= 1:
                      return [l]
        r = []
        for i in range(len(l)):
                 s = l[:i] + l[i+1:]
                 p = perm(s)
                 for x in p:
                  r.append(l[i:i+1] + x)
        return r

다음 예는 여러 가지 들여쓰기 에러를 보여줍니다:

    def perm(l):                       # 에러: 첫 줄을 들여쓰기 했습니다
    for i in range(len(l)):             # 에러: 들여쓰지 않았습니다
        s = l[:i] + l[i+1:]
            p = perm(l[:i] + l[i+1:])   # 에러: 예기치 않은 들여쓰기
            for x in p:
                    r.append(l[i:i+1] + x)
                return r                # 에러: 일관성 없는 내어쓰기

(사실, 처음 세 개의 에러는 파서가 감지합니다. 단지 마지막 에러만 어휘 분석기가 감지합니다. — `return r` 의 들여쓰기가 스택에 있는 값과 일치하지 않습니다.)

### 2.1.9. 토큰 사이의 공백

Except at the beginning of a logical line or in string literals, the whitespace characters space, tab and formfeed can be used interchangeably to separate tokens:

    whitespace:  ' ' | tab | formfeed

Whitespace is needed between two tokens only if their concatenation could otherwise be interpreted as a different token. For example, `ab` is one token, but `a b` is two tokens. However, `+a` and `+ a` both produce two tokens, `+` and `a`, as `+a` is not a valid token.

### 2.1.10. End marker

At the end of non-interactive input, the lexical analyzer generates an `ENDMARKER` token.

## 2.2. 다른 토큰들

Besides `NEWLINE`, `INDENT` and `DEDENT`, the following categories of tokens exist: identifiers and keywords (`NAME`), literals (such as `NUMBER` and `STRING`), and other symbols (operators and delimiters, `OP`). Whitespace characters (other than logical line terminators, discussed earlier) are not tokens, but serve to delimit tokens. Where ambiguity exists, a token comprises the longest possible string that forms a legal token, when read from left to right.

## 2.3. Names (identifiers and keywords)

`NAME` tokens represent identifiers, keywords, and soft keywords.

Names are composed of the following characters:

- uppercase and lowercase letters (`A-Z` and `a-z`),

- the underscore (`_`),

- digits (`0` through `9`), which cannot appear as the first character, and

- non-ASCII characters. Valid names may only contain “letter-like” and “digit-like” characters; see Non-ASCII characters in names for details.

Names must contain at least one character, but have no upper length limit. Case is significant.

Formally, names are described by the following lexical definitions:

    NAME:          name_start name_continue*
    name_start:    "a"..."z" | "A"..."Z" | "_" | <non-ASCII character>
    name_continue: name_start | "0"..."9"
    identifier:    <NAME, except keywords>

Note that not all names matched by this grammar are valid; see Non-ASCII characters in names for details.

### 2.3.1. 키워드

The following names are used as reserved words, or keywords of the language, and cannot be used as ordinary identifiers. They must be spelled exactly as written here:

    False      await      else       import     pass
    None       break      except     in         raise
    True       class      finally    is         return
    and        continue   for        lambda     try
    as         def        from       nonlocal   while
    assert     del        global     not        with
    async      elif       if         or         yield

### 2.3.2. 소프트 키워드

Added in version 3.10.

Some names are only reserved under specific contexts. These are known as soft keywords:

- `match`, `case`, and `_`, when used in the `match` statement.

- `type`, when used in the `type` statement.

These syntactically act as keywords in their specific contexts, but this distinction is done at the parser level, not when tokenizing.

As soft keywords, their use in the grammar is possible while still preserving compatibility with existing code that uses these names as identifier names.

버전 3.12에서 변경: `type` is now a soft keyword.

### 2.3.3. 식별자의 예약 영역

(키워드와는 별개로) 어떤 부류의 식별자들은 특별한 의미가 있습니다. 이 부류의 식별자들은 시작과 끝의 밑줄 문자 패턴으로 구분됩니다:

`_*`

  `from module import *` 에 의해 임포트되지 않습니다.

`_`

  In a `case` pattern within a `match` statement, `_` is a soft keyword that denotes a wildcard.

  한편, 대화형 인터프리터는 마지막 평가 결과물을 변수 `_`에 저장합니다. (`print` 와 같은 내장 함수와 함께, `builtins` 모듈에 저장됩니다.)

  Elsewhere, `_` is a regular identifier. It is often used to name “special” items, but it is not special to Python itself.

  참고

  이름 `_` 은 종종 국제화(internationalization)와 관련되어 사용됩니다. 이 관례에 관해서는 `gettext` 모듈의 문서를 참조하십시오.

  It is also commonly used for unused variables.

`__*__`

  시스템 정의 이름, 비공식적으로 “던더(dunder)” 이름이라고 알려졌습니다. 이 이름들은 인터프리터와 그 구현(표준 라이브러리를 포함합니다)이 정의합니다. 현재 정의된 시스템 이름은 특수 메서드 이름들 섹션과 그 외의 곳에서 논의됩니다. 파이썬의 미래 버전에서는 더 많은 것들이 정의될 가능성이 큽니다. 어떤 문맥에서건, 명시적으로 문서로 만들어진 사용법을 벗어나는 `__*__` 이름의 모든 사용은, 경고 없이 손상될 수 있습니다.

`__*`

  클래스-비공개 이름. 이 부류의 이름들을 클래스 정의 문맥에서 사용하면 뒤섞인 형태로 변형됩니다. 부모 클래스와 자식 클래스의 “비공개(private)” 어트리뷰트 간의 이름 충돌을 피하기 위함입니다. 식별자 (이름) 섹션을 보세요.

### 2.3.4. Non-ASCII characters in names

Names that contain non-ASCII characters need additional normalization and validation beyond the rules and grammar explained above. For example, `ř_1`, `蛇`, or `साँप` are valid names, but `r〰2`, `€`, or `🐍` are not.

This section explains the exact rules.

All names are converted into the normalization form NFKC while parsing. This means that, for example, some typographic variants of characters are converted to their “basic” form. For example, `ﬁⁿₐˡᵢᶻₐᵗᵢᵒₙ` normalizes to `finalization`, so Python treats them as the same name:

    >>> ﬁⁿₐˡᵢᶻₐᵗᵢᵒₙ = 3
    >>> finalization
    3

참고

Normalization is done at the lexical level only. Run-time functions that take names as strings generally do not normalize their arguments. For example, the variable defined above is accessible at run time in the `globals()` dictionary as `globals()["finalization"]` but not `globals()["ﬁⁿₐˡᵢᶻₐᵗᵢᵒₙ"]`.

Similarly to how ASCII-only names must contain only letters, digits and the underscore, and cannot start with a digit, a valid name must start with a character in the “letter-like” set `xid_start`, and the remaining characters must be in the “letter- and digit-like” set `xid_continue`.

These sets based on the XID_Start and XID_Continue sets as defined by the Unicode standard annex UAX-31. Python’s `xid_start` additionally includes the underscore (`_`). Note that Python does not necessarily conform to UAX-31.

A non-normative listing of characters in the XID_Start and XID_Continue sets as defined by Unicode is available in the DerivedCoreProperties.txt file in the Unicode Character Database. For reference, the construction rules for the `xid_*` sets are given below.

The set `id_start` is defined as the union of:

- Unicode category `<Lu>` - uppercase letters (includes `A` to `Z`)

- Unicode category `<Ll>` - lowercase letters (includes `a` to `z`)

- Unicode category `<Lt>` - titlecase letters

- Unicode category `<Lm>` - modifier letters

- Unicode category `<Lo>` - other letters

- Unicode category `<Nl>` - letter numbers

- {`"_"`} - the underscore

- `<Other_ID_Start>` - an explicit set of characters in PropList.txt to support backwards compatibility

The set `xid_start` then closes this set under NFKC normalization, by removing all characters whose normalization is not of the form `id_start id_continue*`.

The set `id_continue` is defined as the union of:

- `id_start` (see above)

- Unicode category `<Nd>` - decimal numbers (includes `0` to `9`)

- Unicode category `<Pc>` - connector punctuations

- Unicode category `<Mn>` - nonspacing marks

- Unicode category `<Mc>` - spacing combining marks

- `<Other_ID_Continue>` - another explicit set of characters in PropList.txt to support backwards compatibility

Again, `xid_continue` closes this set under NFKC normalization.

Unicode categories use the version of the Unicode Character Database as included in the `unicodedata` module.

더 보기

- PEP 3131 – Supporting Non-ASCII Identifiers

- PEP 672 – Unicode-related Security Considerations for Python

## 2.4. 리터럴

리터럴(literal)은 몇몇 내장형들의 상숫값을 위한 표기법입니다.

In terms of lexical analysis, Python has string, bytes and numeric literals.

Other “literals” are lexically denoted using keywords (`None`, `True`, `False`) and the special ellipsis token (`...`).

## 2.5. 문자열과 바이트열 리터럴

String literals are text enclosed in single quotes (`'`) or double quotes (`"`). For example:

    "spam"
    'eggs'

The quote used to start the literal also terminates it, so a string literal can only contain the other quote (except with escape sequences, see below). For example:

    'Say "Hello", please.'
    "Don't do that!"

Except for this limitation, the choice of quote character (`'` or `"`) does not affect how the literal is parsed.

Inside a string literal, the backslash (`\`) character introduces an escape sequence, which has special meaning depending on the character after the backslash. For example, `\"` denotes the double quote character, and does not end the string:

    >>> print("Say \"Hello\" to everyone!")
    Say "Hello" to everyone!

See escape sequences below for a full list of such sequences, and more details.

### 2.5.1. Triple-quoted strings

Strings can also be enclosed in matching groups of three single or double quotes. These are generally referred to as triple-quoted strings:

    """This is a triple-quoted string."""

In triple-quoted literals, unescaped quotes are allowed (and are retained), except that three unescaped quotes in a row terminate the literal, if they are of the same kind (`'` or `"`) used at the start:

    """This string has "quotes" inside."""

Unescaped newlines are also allowed and retained:

    '''This triple-quoted string
    continues on the next line.'''

### 2.5.2. String prefixes

String literals can have an optional prefix that influences how the content of the literal is parsed, for example:

    b"data"
    f'{result=}'

The allowed prefixes are:

- `b`: Bytes literal

- `r`: Raw string

- `f`: Formatted string literal (“f-string”)

- `t`: Template string literal (“t-string”)

- `u`: No effect (allowed for backwards compatibility)

See the linked sections for details on each type.

Prefixes are case-insensitive (for example, ‘`B`’ works the same as ‘`b`’). The ‘`r`’ prefix can be combined with ‘`f`’, ‘`t`’ or ‘`b`’, so ‘`fr`’, ‘`rf`’, ‘`tr`’, ‘`rt`’, ‘`br`’, and ‘`rb`’ are also valid prefixes.

Added in version 3.3: 날 바이트열 리터럴의 `'br'` 와 같은 의미가 있는 `'rb'` 접두어가 추가되었습니다.

파이썬 2.x 와 3.x 에서 동시에 지원하는 코드들의 유지보수를 단순화하기 위해 예전에 사용되던 유니코드 리터럴 (`u'value'`)이 다시 도입되었습니다. 자세한 정보는 PEP 414 에 나옵니다.

### 2.5.3. Formal grammar

String literals, except “f-strings” and “t-strings”, are described by the following lexical definitions.

These definitions use negative lookaheads (`!`) to indicate that an ending quote ends the literal.

    STRING:          [stringprefix] (stringcontent)
    stringprefix:    <("r" | "u" | "b" | "br" | "rb"), case-insensitive>
    stringcontent:
       | "'''" ( !"'''" longstringitem)* "'''"
       | '"""' ( !'"""' longstringitem)* '"""'
       | "'" ( !"'" stringitem)* "'"
       | '"' ( !'"' stringitem)* '"'
    stringitem:      stringchar | stringescapeseq
    stringchar:      <any source_character, except backslash and newline>
    longstringitem:  stringitem | newline
    stringescapeseq: "\" <any source_character>

Note that as in all lexical definitions, whitespace is significant. In particular, the prefix (if any) must be immediately followed by the starting quote.

### 2.5.4. 이스케이프 시퀀스

Unless an ‘`r`’ or ‘`R`’ prefix is present, escape sequences in string and bytes literals are interpreted according to rules similar to those used by Standard C. The recognized escape sequences are:

이스케이프 시퀀스 | 의미
--- | ---
`\`<newline> | Ignored end of line
`\\` | Backslash
`\'` | Single quote
`\"` | Double quote
`\a` | ASCII 벨 (BEL)
`\b` | ASCII 백스페이스 (BS)
`\f` | ASCII 폼 피드 (FF)
`\n` | ASCII 라인 피드 (LF)
`\r` | ASCII 캐리지 리턴 (CR)
`\t` | ASCII 가로 탭 (TAB)
`\v` | ASCII 세로 탭 (VT)
`\ooo` | Octal character
`\xhh` | Hexadecimal character
`\N{name}` | Named Unicode character
`\uxxxx` | Hexadecimal Unicode character
`\Uxxxxxxxx` | Hexadecimal Unicode character

#### 2.5.4.1. Ignored end of line

A backslash can be added at the end of a line to ignore the newline:

    >>> 'This string will not include \
    ... backslashes or newline characters.'
    'This string will not include backslashes or newline characters.'

The same result can be achieved using triple-quoted strings, or parentheses and string literal concatenation.

#### 2.5.4.2. Escaped characters

To include a backslash in a non-raw Python string literal, it must be doubled. The `\\` escape sequence denotes a single backslash character:

    >>> print('C:\\Program Files')
    C:\Program Files

Similarly, the `\'` and `\"` sequences denote the single and double quote character, respectively:

    >>> print('\' and \"')
    ' and "

#### 2.5.4.3. Octal character

The sequence `\ooo` denotes a character with the octal (base 8) value ooo:

    >>> '\120'
    'P'

Up to three octal digits (0 through 7) are accepted.

In a bytes literal, character means a byte with the given value. In a string literal, it means a Unicode character with the given value.

버전 3.11에서 변경: Octal escapes with value larger than `0o377` (255) produce a `DeprecationWarning`.

버전 3.12에서 변경: Octal escapes with value larger than `0o377` (255) produce a `SyntaxWarning`. In a future Python version they will raise a `SyntaxError`.

#### 2.5.4.4. Hexadecimal character

The sequence `\xhh` denotes a character with the hex (base 16) value hh:

    >>> '\x50'
    'P'

표준 C와는 달리, 정확히 두 개의 16진수가 제공되어야 합니다.

In a bytes literal, character means a byte with the given value. In a string literal, it means a Unicode character with the given value.

#### 2.5.4.5. Named Unicode character

The sequence `\N{name}` denotes a Unicode character with the given name:

    >>> '\N{LATIN CAPITAL LETTER P}'
    'P'
    >>> '\N{SNAKE}'
    '🐍'

This sequence cannot appear in bytes literals.

버전 3.3에서 변경: Support for name aliases has been added.

#### 2.5.4.6. Hexadecimal Unicode characters

These sequences `\uxxxx` and `\Uxxxxxxxx` denote the Unicode character with the given hex (base 16) value. Exactly four digits are required for `\u`; exactly eight digits are required for `\U`. The latter can encode any Unicode character.

    >>> '\u1234'
    'ሴ'
    >>> '\U0001f40d'
    '🐍'

These sequences cannot appear in bytes literals.

#### 2.5.4.7. Unrecognized escape sequences

Unlike in Standard C, all unrecognized escape sequences are left in the string unchanged, that is, the backslash is left in the result:

    >>> print('\q')
    \q
    >>> list('\q')
    ['\\', 'q']

Note that for bytes literals, the escape sequences only recognized in string literals (`\N...`, `\u...`, `\U...`) fall into the category of unrecognized escapes.

버전 3.6에서 변경: Unrecognized escape sequences produce a `DeprecationWarning`.

버전 3.12에서 변경: Unrecognized escape sequences produce a `SyntaxWarning`. In a future Python version they will raise a `SyntaxError`.

### 2.5.5. Bytes literals

Bytes literals are always prefixed with ‘`b`’ or ‘`B`’; they produce an instance of the `bytes` type instead of the `str` type. They may only contain ASCII characters; bytes with a numeric value of 128 or greater must be expressed with escape sequences (typically Hexadecimal character or Octal character):

    >>> b'\x89PNG\r\n\x1a\n'
    b'\x89PNG\r\n\x1a\n'
    >>> list(b'\x89PNG\r\n\x1a\n')
    [137, 80, 78, 71, 13, 10, 26, 10]

Similarly, a zero byte must be expressed using an escape sequence (typically `\0` or `\x00`).

### 2.5.6. Raw string literals

Both string and bytes literals may optionally be prefixed with a letter ‘`r`’ or ‘`R`’; such constructs are called raw string literals and raw bytes literals respectively and treat backslashes as literal characters. As a result, in raw string literals, escape sequences are not treated specially:

    >>> r'\d{4}-\d{2}-\d{2}'
    '\\d{4}-\\d{2}-\\d{2}'

날 리터럴에서 조차, 따옴표는 역 슬래시로 이스케이프 됩니다. 하지만 역 슬래시가 결과에 남게 됩니다; 예를 들어, `r"\""` 는 올바른 문자열 리터럴인데, 두 개의 문자가 들어있습니다: 역 슬래시와 큰따옴표; `r"\"` 는 올바른 문자열 리터럴이 아닙니다 (날 문자열조차 홀수개의 역 슬래시로 끝날 수 없습니다.). 좀 더 명확하게 말하자면, 날 리터럴은 하나의 역 슬래시로 끝날 수 없습니다(역 슬래시가 뒤에 오는 따옴표를 이스케이프 시키기 때문입니다). 역 슬래시와 바로 뒤에 오는 개행문자는 줄 결합이 아니라 리터럴에 포함되는 두 개의 문자로 인식됨에 주의해야 합니다.

### 2.5.7. 포맷 문자열 리터럴

Added in version 3.6.

버전 3.7에서 변경: The `await` and `async for` can be used in expressions within f-strings.

버전 3.8에서 변경: Added the debug specifier (`=`)

버전 3.12에서 변경: Many restrictions on expressions within f-strings have been removed. Notably, nested strings, comments, and backslashes are now permitted.

A formatted string literal or f-string is a string literal that is prefixed with ‘`f`’ or ‘`F`’. Unlike other string literals, f-strings do not have a constant value. They may contain replacement fields delimited by curly braces `{}`. Replacement fields contain expressions which are evaluated at run time. For example:

    >>> who = 'nobody'
    >>> nationality = 'Spanish'
    >>> f'{who.title()} expects the {nationality} Inquisition!'
    'Nobody expects the Spanish Inquisition!'

Any doubled curly braces (`{{` or `}}`) outside replacement fields are replaced with the corresponding single curly brace:

    >>> print(f'{{...}}')
    {...}

Other characters outside replacement fields are treated like in ordinary string literals. This means that escape sequences are decoded (except when a literal is also marked as a raw string), and newlines are possible in triple-quoted f-strings:

    >>> name = 'Galahad'
    >>> favorite_color = 'blue'
    >>> print(f'{name}:\t{favorite_color}')
    Galahad:       blue
    >>> print(rf"C:\Users\{name}")
    C:\Users\Galahad
    >>> print(f'''Three shall be the number of the counting
    ... and the number of the counting shall be three.''')
    Three shall be the number of the counting
    and the number of the counting shall be three.

Expressions in formatted string literals are treated like regular Python expressions. Each expression is evaluated in the context where the formatted string literal appears, in order from left to right. An empty expression is not allowed, and both `lambda` and assignment expressions `:=` must be surrounded by explicit parentheses:

    >>> f'{(half := 1/2)}, {half * 42}'
    '0.5, 21.0'

Reusing the outer f-string quoting type inside a replacement field is permitted:

    >>> a = dict(x=2)
    >>> f"abc {a["x"]} def"
    'abc 2 def'

Backslashes are also allowed in replacement fields and are evaluated the same way as in any other context:

    >>> a = ["a", "b", "c"]
    >>> print(f"List a contains:\n{"\n".join(a)}")
    List a contains:
    a
    b
    c

It is possible to nest f-strings:

    >>> name = 'world'
    >>> f'Repeated:{f' hello {name}' * 3}'
    'Repeated: hello world hello world hello world'

Portable Python programs should not use more than 5 levels of nesting.

CPython 구현 상세: CPython does not limit nesting of f-strings.

Replacement expressions can contain newlines in both single-quoted and triple-quoted f-strings and they can contain comments. Everything that comes after a `#` inside a replacement field is a comment (even closing braces and quotes). This means that replacement fields with comments must be closed in a different line:

    >>> a = 2
    >>> f"abc{a  # This comment  }"  continues until the end of the line
    ...       + 3}"
    'abc5'

After the expression, replacement fields may optionally contain:

- a debug specifier – an equal sign (`=`), optionally surrounded by whitespace on one or both sides;

- a conversion specifier – `!s`, `!r` or `!a`; and/or

- a format specifier prefixed with a colon (`:`).

See the Standard Library section on f-strings for details on how these fields are evaluated.

As that section explains, format specifiers are passed as the second argument to the `format()` function to format a replacement field value. For example, they can be used to specify a field width and padding characters using the Format Specification Mini-Language:

    >>> number = 14.3
    >>> f'{number:20.7f}'
    '          14.3000000'

Top-level format specifiers may include nested replacement fields:

    >>> field_size = 20
    >>> precision = 7
    >>> f'{number:{field_size}.{precision}f}'
    '          14.3000000'

These nested fields may include their own conversion fields and format specifiers:

    >>> number = 3
    >>> f'{number:{field_size}}'
    '                   3'
    >>> f'{number:{field_size:05}}'
    '00000000000000000003'

However, these nested fields may not include more deeply nested replacement fields.

Formatted string literals cannot be used as docstrings, even if they do not include expressions:

    >>> def foo():
    ...     f"Not a docstring"
    ...
    >>> print(foo.__doc__)
    None

더 보기

- PEP 498 – Literal String Interpolation

- PEP 701 – Syntactic formalization of f-strings

- `str.format()`, which uses a related format string mechanism.

### 2.5.8. t-strings

Added in version 3.14.

A template string literal or t-string is a string literal that is prefixed with ‘`t`’ or ‘`T`’. These strings follow the same syntax rules as formatted string literals. For differences in evaluation rules, see the Standard Library section on t-strings

### 2.5.9. Formal grammar for f-strings

F-strings are handled partly by the lexical analyzer, which produces the tokens `FSTRING_START`, `FSTRING_MIDDLE` and `FSTRING_END`, and partly by the parser, which handles expressions in the replacement field. The exact way the work is split is a CPython implementation detail.

Correspondingly, the f-string grammar is a mix of lexical and syntactic definitions.

Whitespace is significant in these situations:

- There may be no whitespace in `FSTRING_START` (between the prefix and quote).

- Whitespace in `FSTRING_MIDDLE` is part of the literal string contents.

- In `fstring_replacement_field`, if `f_debug_specifier` is present, all whitespace after the opening brace until the `f_debug_specifier`, as well as whitespace immediately following `f_debug_specifier`, is retained as part of the expression.

  CPython 구현 상세: The expression is not handled in the tokenization phase; it is retrieved from the source code using locations of the `{` token and the token after `=`.

The `FSTRING_MIDDLE` definition uses negative lookaheads (`!`) to indicate special characters (backslash, newline, `{`, `}`) and sequences (`f_quote`).

    fstring:    FSTRING_START fstring_middle* FSTRING_END

    FSTRING_START:      fstringprefix ("'" | '"' | "'''" | '"""')
    FSTRING_END:        f_quote
    fstringprefix:      <("f" | "fr" | "rf"), case-insensitive>
    f_debug_specifier:  '='
    f_quote:            <the quote character(s) used in FSTRING_START>

    fstring_middle:
       | fstring_replacement_field
       | FSTRING_MIDDLE
    FSTRING_MIDDLE:
       | (!"\" !newline !'{' !'}' !f_quote) source_character
       | stringescapeseq
       | "{{"
       | "}}"
       | <newline, in triple-quoted f-strings only>
    fstring_replacement_field:
       | '{' f_expression [f_debug_specifier] [fstring_conversion]
             [fstring_full_format_spec] '}'
    fstring_conversion:
       | "!" ("s" | "r" | "a")
    fstring_full_format_spec:
       | ':' fstring_format_spec*
    fstring_format_spec:
       | FSTRING_MIDDLE
       | fstring_replacement_field
    f_expression:
       | ','.(conditional_expression | "*" or_expr)+ [","]
       | yield_expression

참고

In the above grammar snippet, the `f_quote` and `FSTRING_MIDDLE` rules are context-sensitive – they depend on the contents of `FSTRING_START` of the nearest enclosing `fstring`.

Constructing a more traditional formal grammar from this template is left as an exercise for the reader.

The grammar for t-strings is identical to the one for f-strings, with t instead of f at the beginning of rule and token names and in the prefix.

    tstring:    TSTRING_START tstring_middle* TSTRING_END

    <rest of the t-string grammar is omitted; see above>

## 2.6. 숫자 리터럴

`NUMBER` tokens represent numeric literals, of which there are three types: integers, floating-point numbers, and imaginary numbers.

    NUMBER: integer | floatnumber | imagnumber

The numeric value of a numeric literal is the same as if it were passed as a string to the `int`, `float` or `complex` class constructor, respectively. Note that not all valid inputs for those constructors are also valid literals.

Numeric literals do not include a sign; a phrase like `-1` is actually an expression composed of the unary operator ‘`-`’ and the literal `1`.

### 2.6.1. 정수 리터럴

Integer literals denote whole numbers. For example:

    7
    3
    2147483647

There is no limit for the length of integer literals apart from what can be stored in available memory:

    7922816251426433759354395033679228162514264337593543950336

Underscores can be used to group digits for enhanced readability, and are ignored for determining the numeric value of the literal. For example, the following literals are equivalent:

    100_000_000_000
    100000000000
    1_00_00_00_00_000

Underscores can only occur between digits. For example, `_123`, `321_`, and `123__321` are not valid literals.

Integers can be specified in binary (base 2), octal (base 8), or hexadecimal (base 16) using the prefixes `0b`, `0o` and `0x`, respectively. Hexadecimal digits 10 through 15 are represented by letters `A`-`F`, case-insensitive. For example:

    0b100110111
    0b_1110_0101
    0o177
    0o377
    0xdeadbeef
    0xDead_Beef

An underscore can follow the base specifier. For example, `0x_1f` is a valid literal, but `0_x1f` and `0x__1f` are not.

Leading zeros in a non-zero decimal number are not allowed. For example, `0123` is not a valid literal. This is for disambiguation with C-style octal literals, which Python used before version 3.0.

Formally, integer literals are described by the following lexical definitions:

    integer:      decinteger | bininteger | octinteger | hexinteger | zerointeger
    decinteger:   nonzerodigit (["_"] digit)*
    bininteger:   "0" ("b" | "B") (["_"] bindigit)+
    octinteger:   "0" ("o" | "O") (["_"] octdigit)+
    hexinteger:   "0" ("x" | "X") (["_"] hexdigit)+
    zerointeger:  "0"+ (["_"] "0")*
    nonzerodigit: "1"..."9"
    digit:        "0"..."9"
    bindigit:     "0" | "1"
    octdigit:     "0"..."7"
    hexdigit:     digit | "a"..."f" | "A"..."F"

버전 3.6에서 변경: 리터럴에서 숫자들의 그룹을 표현할 목적으로 밑줄을 허락합니다.

### 2.6.2. 실수 리터럴

Floating-point (float) literals, such as `3.14` or `1.5`, denote approximations of real numbers.

They consist of integer and fraction parts, each composed of decimal digits. The parts are separated by a decimal point, `.`:

    2.71828
    4.0

Unlike in integer literals, leading zeros are allowed. For example, `077.010` is legal, and denotes the same number as `77.01`.

As in integer literals, single underscores may occur between digits to help readability:

    96_485.332_123
    3.14_15_93

Either of these parts, but not both, can be empty. For example:

    10.  # (equivalent to 10.0)
    .001  # (equivalent to 0.001)

Optionally, the integer and fraction may be followed by an exponent: the letter `e` or `E`, followed by an optional sign, `+` or `-`, and a number in the same format as the integer and fraction parts. The `e` or `E` represents “times ten raised to the power of”:

    1.0e3  # (represents 1.0×10³, or 1000.0)
    1.166e-5  # (represents 1.166×10⁻⁵, or 0.00001166)
    6.02214076e+23  # (represents 6.02214076×10²³, or 602214076000000000000000.)

In floats with only integer and exponent parts, the decimal point may be omitted:

    1e3  # (equivalent to 1.e3 and 1.0e3)
    0e0  # (equivalent to 0.)

Formally, floating-point literals are described by the following lexical definitions:

    floatnumber:
       | digitpart "." [digitpart] [exponent]
       | "." digitpart [exponent]
       | digitpart exponent
    digitpart: digit (["_"] digit)*
    exponent:  ("e" | "E") ["+" | "-"] digitpart

버전 3.6에서 변경: 리터럴에서 숫자들의 그룹을 표현할 목적으로 밑줄을 허락합니다.

### 2.6.3. 허수 리터럴

Python has complex number objects, but no complex literals. Instead, imaginary literals denote complex numbers with a zero real part.

For example, in math, the complex number 3+4.2i is written as the real number 3 added to the imaginary number 4.2i. Python uses a similar syntax, except the imaginary unit is written as `j` rather than i:

    3+4.2j

This is an expression composed of the integer literal `3`, the operator ‘`+`’, and the imaginary literal `4.2j`. Since these are three separate tokens, whitespace is allowed between them:

    3 + 4.2j

No whitespace is allowed within each token. In particular, the `j` suffix, may not be separated from the number before it.

The number before the `j` has the same syntax as a floating-point literal. Thus, the following are valid imaginary literals:

    4.2j
    3.14j
    10.j
    .001j
    1e100j
    3.14e-10j
    3.14_15_93j

Unlike in a floating-point literal the decimal point can be omitted if the imaginary number only has an integer part. The number is still evaluated as a floating-point number, not an integer:

    10j
    0j
    1000000000000000000000000j   # equivalent to 1e+24j

The `j` suffix is case-insensitive. That means you can use `J` instead:

    3.14J   # equivalent to 3.14j

Formally, imaginary literals are described by the following lexical definition:

    imagnumber: (floatnumber | digitpart) ("j" | "J")

## 2.7. Operators and delimiters

The following grammar defines operator and delimiter tokens, that is, the generic `OP` token type. A list of these tokens and their names is also available in the `token` module documentation.

    OP:
       | assignment_operator
       | bitwise_operator
       | comparison_operator
       | enclosing_delimiter
       | other_delimiter
       | arithmetic_operator
       | "..."
       | other_op

    assignment_operator:   "+=" | "-=" | "*=" | "**=" | "/="  | "//=" | "%=" |
                           "&=" | "|=" | "^=" | "<<=" | ">>=" | "@="  | ":="
    bitwise_operator:      "&"  | "|"  | "^"  | "~"   | "<<"  | ">>"
    comparison_operator:   "<=" | ">=" | "<"  | ">"   | "=="  | "!="
    enclosing_delimiter:   "("  | ")"  | "["  | "]"   | "{"   | "}"
    other_delimiter:       ","  | ":"  | "!"  | ";"   | "="   | "->"
    arithmetic_operator:   "+"  | "-"  | "**" | "*"   | "//"  | "/"   | "%"
    other_op:              "."  | "@"

참고

Generally, operators are used to combine expressions, while delimiters serve other purposes. However, there is no clear, formal distinction between the two categories.

Some tokens can serve as either operators or delimiters, depending on usage. For example, `*` is both the multiplication operator and a delimiter used for sequence unpacking, and `@` is both the matrix multiplication and a delimiter that introduces decorators.

For some tokens, the distinction is unclear. For example, some people consider `.`, `(`, and `)` to be delimiters, while others see the `getattr()` operator and the function call operator(s).

Some of Python’s operators, like `and`, `or`, and `not in`, use keyword tokens rather than “symbols” (operator tokens).

A sequence of three consecutive periods (`...`) has a special meaning as an `Ellipsis` literal.