4. 深入了解流程控制¶
除了剛才介紹的 while
,Python 擁有在其他程式語言中常用的流程控制語法,並有ㄧ些不一樣的改變。
4.1. if
语句¶
或許最常見的陳述式種類就是 if
了。舉例來說:
>>> x = int(input("Please enter an integer: "))
Please enter an integer: 42
>>> if x < 0:
... x = 0
... print('Negative changed to zero')
... elif x == 0:
... print('Zero')
... elif x == 1:
... print('Single')
... else:
... print('More')
...
More
可以有零个或多个 elif
部分,以及一个可选的 else
部分。 关键字 'elif
' 是 'else if' 的缩写,适合用于避免过多的缩进。 一个 if
... elif
... elif
... 序列可以看作是其他语言中的 switch
或 case
语句的替代。
4.2. for
语句¶
Python 中的 for
语句与你在 C 或 Pascal 中可能用到的有所不同。 Python 中的 for
语句并不总是对算术递增的数值进行迭代(如同 Pascal),或是给予用户定义迭代步骤和暂停条件的能力(如同 C),而是对任意序列进行迭代(例如列表或字符串),条目的迭代顺序与它们在序列中出现的顺序一致。 例如(此处英文为双关语):
>>> # Measure some strings:
... words = ['cat', 'window', 'defenestrate']
>>> for w in words:
... print(w, len(w))
...
cat 3
window 6
defenestrate 12
如果你在迴圈中需要修改一個你正在疊代的序列(例如重複一些選擇的元素),那麼會建議你先建立一個序列的拷貝。疊代序列並不暗示建立新的拷貝。此時 slice 語法就讓這件事十分容易完成:
>>> for w in words[:]: # Loop over a slice copy of the entire list.
... if len(w) > 6:
... words.insert(0, w)
...
>>> words
['defenestrate', 'cat', 'window', 'defenestrate']
在 for w in words:
的情況,這個例子會試著重覆不斷地插入 defenestrate
,產生一個無限長的 list。
4.3. range()
函式¶
如果你需要疊代一個數列的話,使用內建 range()
函式就很方便。它可以生成一等差級數:
>>> for i in range(5):
... print(i)
...
0
1
2
3
4
給定的結束值永遠不會出現在生成的序列中;range(10)
生成的 10 個數值,即對應存取一個長度為 10 的序列內每一個元素的索引值。也可以讓 range 從其他數值計數,或者給定不同的級距(甚至為負;有時稱之為 step):
range(5, 10)
5, 6, 7, 8, 9
range(0, 10, 3)
0, 3, 6, 9
range(-10, -100, -30)
-10, -40, -70
欲疊代一個序列的索引值,你可以搭配使用 range()
和 len()
如下:
>>> a = ['Mary', 'had', 'a', 'little', 'lamb']
>>> for i in range(len(a)):
... print(i, a[i])
...
0 Mary
1 had
2 a
3 little
4 lamb
然而,在多數的情況,使用 enumerate()
函式將更為方便,詳見迴圈技巧。
如果直接印出一個 range 則會出現奇怪的輸出:
>>> print(range(10))
range(0, 10)
在很多情況下,由 range()
回傳的物件的行為如同一個 list,但實際上它並不是。它是一個物件在你疊代時會回傳想要的序列的連續元素,並不會真正建出這個序列的 list,以節省空間。
We say such an object is iterable, that is, suitable as a target for
functions and constructs that expect something from which they can
obtain successive items until the supply is exhausted. We have seen that
the for
statement is such a construct, while an example of function
that takes an iterable is sum()
:
>>> sum(range(4)) # 0 + 1 + 2 + 3
6
Later we will see more functions that return iterables and take iterables as arguments. Lastly, maybe you are curious about how to get a list from a range. Here is the solution:
>>> list(range(4))
[0, 1, 2, 3]
In chapter 資料結構, we will discuss in more detail about
list()
.
4.4. break
和 continue
语句,以及循环中的 else
子句¶
break
陳述,如同 C 語言,終止包含其最內部的 for
或 while
迴圈。
Loop statements may have an else
clause; it is executed when the loop
terminates through exhaustion of the iterable (with for
) or when the
condition becomes false (with while
), but not when the loop is
terminated by a break
statement. This is exemplified by the
following loop, which searches for prime numbers:
>>> for n in range(2, 10):
... for x in range(2, n):
... if n % x == 0:
... print(n, 'equals', x, '*', n//x)
... break
... else:
... # loop fell through without finding a factor
... print(n, 'is a prime number')
...
2 is a prime number
3 is a prime number
4 equals 2 * 2
5 is a prime number
6 equals 2 * 3
7 is a prime number
8 equals 2 * 4
9 equals 3 * 3
(沒錯,這是正確的程式碼。請看仔細:else
段落屬於 for
迴圈,並非 if
陳述。)
When used with a loop, the else
clause has more in common with the
else
clause of a try
statement than it does with that of
if
statements: a try
statement's else
clause runs
when no exception occurs, and a loop's else
clause runs when no break
occurs. For more on the try
statement and exceptions, see
處理例外.
continue
陳述,亦承襲於 C 語言,讓所屬的迴圈繼續執行下個疊代:
>>> for num in range(2, 10):
... if num % 2 == 0:
... print("Found an even number", num)
... continue
... print("Found a number", num)
Found an even number 2
Found a number 3
Found an even number 4
Found a number 5
Found an even number 6
Found a number 7
Found an even number 8
Found a number 9
4.5. pass
语句¶
pass
陳述不執行任何動作。它用在語法上需要一個陳述但不需要執行任何動作的時候。例如:
>>> while True:
... pass # Busy-wait for keyboard interrupt (Ctrl+C)
...
這經常用於定義一個最簡單的類別:
>>> class MyEmptyClass:
... pass
...
pass
的另一个可以使用的场合是在你编写新的代码时作为一个函数或条件子句体的占位符,允许你保持在更抽象的层次上进行思考。 pass
会被静默地忽略:
>>> def initlog(*args):
... pass # Remember to implement this!
...
4.6. 定義函式 (function)¶
我們可以建立一個函式來產生費式數列到任何一個上界:
>>> def fib(n): # write Fibonacci series up to n
... """Print a Fibonacci series up to n."""
... a, b = 0, 1
... while a < n:
... print(a, end=' ')
... a, b = b, a+b
... print()
...
>>> # Now call the function we just defined:
... fib(2000)
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597
關鍵字 def
帶入一個函式的定義。它之後必須連著該函式的名稱和置於括號之中的參數。自下一行起,所有縮排的陳述成為該函式的主體。
一個函式的第一個陳述可以是一個字串值;此情況該字串值被視為該函式的說明文件字串,即 docstring。(關於 docstring 的細節請參見說明文件字串段落。)有些工具可以使用 docstring 來自動產生線上或可列印的文件,或讓使用者能自由地自原始碼中瀏覽文件。在原始碼中加入 docstring 是個好慣例,應該養成這樣的習慣。
The execution of a function introduces a new symbol table used for the local
variables of the function. More precisely, all variable assignments in a
function store the value in the local symbol table; whereas variable references
first look in the local symbol table, then in the local symbol tables of
enclosing functions, then in the global symbol table, and finally in the table
of built-in names. Thus, global variables and variables of enclosing functions
cannot be directly assigned a value within a function (unless, for global
variables, named in a global
statement, or, for variables of enclosing
functions, named in a nonlocal
statement), although they may be
referenced.
在一個函式被呼叫的時候,實際傳入的參數(引數)會被加入至該函數的區域符號表。因此,引數傳入的方式為傳值呼叫 (call by value)(這裡傳遞的「值」永遠是一個物件的參照(reference),而不是該物件的值)。1 當一個函式呼叫別的函式時,在被呼叫的函式中會建立一個新的區域符號表。
一個函式定義會把該函式名稱加入至當前的符號表。該函式名稱的值帶有一個型別,並被直譯器辨識為使用者自定函式(user-defined function)。該值可以被賦予給別的變數名,而該變數也可以被當作函式使用。這即是常見的重新命名方式:
>>> fib
<function fib at 10042ed0>
>>> f = fib
>>> f(100)
0 1 1 2 3 5 8 13 21 34 55 89
如果你是來自別的語言,你可能不同意 fib
是個函式,而是個程序 (procedure),因為它並沒有回傳值。實際上,即使一個函式缺少一個 return
陳述,它亦有一個固定的回傳值。這個值為 None
(它是一個內建名稱)。在直譯器中單獨使用 None
時,通常不會被顯示。你可以使用 print()
來看到它:
>>> fib(0)
>>> print(fib(0))
None
如果要寫一個函式回傳費式數列的 list 而不是直接印出它,這也很容易:
>>> def fib2(n): # return Fibonacci series up to n
... """Return a list containing the Fibonacci series up to n."""
... result = []
... a, b = 0, 1
... while a < n:
... result.append(a) # see below
... a, b = b, a+b
... return result
...
>>> f100 = fib2(100) # call it
>>> f100 # write the result
[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
這個例子一樣示範了一些新的 Python 特性:
return
语句会从函数内部返回一个值。 不带表达式参数的return
会返回None
。 函数执行完毕退出也会返回None
。result.append(a)
陳述呼叫了一個 list 物件的result
method(方法)。method 為「屬於」一個物件的函式,命名規則為obj.methodname
,其中obj
為某個物件(亦可為一表達式),而methodname
為該 method 的名稱,並由該物件的型別所定義。不同的型別代表不同的 method。不同型別的 method 可以擁有一樣的名稱而不會讓 Python 混淆。(你可以使用 class 定義自己的物件型別和 method,見 Classes)這裡append()
method 定義在 list 物件中;它會加入一個新的元素在該 list 的末端。這個例子等同於result = result + [a]
,但更有效率。
4.7. More on Defining Functions¶
It is also possible to define functions with a variable number of arguments. There are three forms, which can be combined.
4.7.1. Default Argument Values¶
The most useful form is to specify a default value for one or more arguments. This creates a function that can be called with fewer arguments than it is defined to allow. For example:
def ask_ok(prompt, retries=4, reminder='Please try again!'):
while True:
ok = input(prompt)
if ok in ('y', 'ye', 'yes'):
return True
if ok in ('n', 'no', 'nop', 'nope'):
return False
retries = retries - 1
if retries < 0:
raise ValueError('invalid user response')
print(reminder)
This function can be called in several ways:
giving only the mandatory argument:
ask_ok('Do you really want to quit?')
giving one of the optional arguments:
ask_ok('OK to overwrite the file?', 2)
or even giving all arguments:
ask_ok('OK to overwrite the file?', 2, 'Come on, only yes or no!')
This example also introduces the in
keyword. This tests whether or
not a sequence contains a certain value.
The default values are evaluated at the point of function definition in the defining scope, so that
i = 5
def f(arg=i):
print(arg)
i = 6
f()
will print 5
.
Important warning: The default value is evaluated only once. This makes a difference when the default is a mutable object such as a list, dictionary, or instances of most classes. For example, the following function accumulates the arguments passed to it on subsequent calls:
def f(a, L=[]):
L.append(a)
return L
print(f(1))
print(f(2))
print(f(3))
This will print
[1]
[1, 2]
[1, 2, 3]
If you don't want the default to be shared between subsequent calls, you can write the function like this instead:
def f(a, L=None):
if L is None:
L = []
L.append(a)
return L
4.7.2. Keyword Arguments¶
Functions can also be called using keyword arguments
of the form kwarg=value
. For instance, the following function:
def parrot(voltage, state='a stiff', action='voom', type='Norwegian Blue'):
print("-- This parrot wouldn't", action, end=' ')
print("if you put", voltage, "volts through it.")
print("-- Lovely plumage, the", type)
print("-- It's", state, "!")
accepts one required argument (voltage
) and three optional arguments
(state
, action
, and type
). This function can be called in any
of the following ways:
parrot(1000) # 1 positional argument
parrot(voltage=1000) # 1 keyword argument
parrot(voltage=1000000, action='VOOOOOM') # 2 keyword arguments
parrot(action='VOOOOOM', voltage=1000000) # 2 keyword arguments
parrot('a million', 'bereft of life', 'jump') # 3 positional arguments
parrot('a thousand', state='pushing up the daisies') # 1 positional, 1 keyword
but all the following calls would be invalid:
parrot() # required argument missing
parrot(voltage=5.0, 'dead') # non-keyword argument after a keyword argument
parrot(110, voltage=220) # duplicate value for the same argument
parrot(actor='John Cleese') # unknown keyword argument
In a function call, keyword arguments must follow positional arguments.
All the keyword arguments passed must match one of the arguments
accepted by the function (e.g. actor
is not a valid argument for the
parrot
function), and their order is not important. This also includes
non-optional arguments (e.g. parrot(voltage=1000)
is valid too).
No argument may receive a value more than once.
Here's an example that fails due to this restriction:
>>> def function(a):
... pass
...
>>> function(0, a=0)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: function() got multiple values for keyword argument 'a'
When a final formal parameter of the form **name
is present, it receives a
dictionary (see Mapping Types --- dict) containing all keyword arguments except for
those corresponding to a formal parameter. This may be combined with a formal
parameter of the form *name
(described in the next subsection) which
receives a tuple containing the positional
arguments beyond the formal parameter list. (*name
must occur
before **name
.) For example, if we define a function like this:
def cheeseshop(kind, *arguments, **keywords):
print("-- Do you have any", kind, "?")
print("-- I'm sorry, we're all out of", kind)
for arg in arguments:
print(arg)
print("-" * 40)
for kw in keywords:
print(kw, ":", keywords[kw])
It could be called like this:
cheeseshop("Limburger", "It's very runny, sir.",
"It's really very, VERY runny, sir.",
shopkeeper="Michael Palin",
client="John Cleese",
sketch="Cheese Shop Sketch")
and of course it would print:
-- Do you have any Limburger ?
-- I'm sorry, we're all out of Limburger
It's very runny, sir.
It's really very, VERY runny, sir.
----------------------------------------
shopkeeper : Michael Palin
client : John Cleese
sketch : Cheese Shop Sketch
Note that the order in which the keyword arguments are printed is guaranteed to match the order in which they were provided in the function call.
4.7.3. Special parameters¶
By default, arguments may be passed to a Python function either by position or explicitly by keyword. For readability and performance, it makes sense to restrict the way arguments can be passed so that a developer need only look at the function definition to determine if items are passed by position, by position or keyword, or by keyword.
A function definition may look like:
def f(pos1, pos2, /, pos_or_kwd, *, kwd1, kwd2):
----------- ---------- ----------
| | |
| Positional or keyword |
| - Keyword only
-- Positional only
where /
and *
are optional. If used, these symbols indicate the kind of
parameter by how the arguments may be passed to the function:
positional-only, positional-or-keyword, and keyword-only. Keyword parameters
are also referred to as named parameters.
4.7.3.1. Positional-or-Keyword Arguments¶
If /
and *
are not present in the function definition, arguments may
be passed to a function by position or by keyword.
4.7.3.2. Positional-Only Parameters¶
Looking at this in a bit more detail, it is possible to mark certain parameters
as positional-only. If positional-only, the parameters' order matters, and
the parameters cannot be passed by keyword. Positional-only parameters are
placed before a /
(forward-slash). The /
is used to logically
separate the positional-only parameters from the rest of the parameters.
If there is no /
in the function definition, there are no positional-only
parameters.
Parameters following the /
may be positional-or-keyword or keyword-only.
4.7.3.3. Keyword-Only Arguments¶
To mark parameters as keyword-only, indicating the parameters must be passed
by keyword argument, place an *
in the arguments list just before the first
keyword-only parameter.
4.7.3.4. Function Examples¶
Consider the following example function definitions paying close attention to the
markers /
and *
:
>>> def standard_arg(arg):
... print(arg)
...
>>> def pos_only_arg(arg, /):
... print(arg)
...
>>> def kwd_only_arg(*, arg):
... print(arg)
...
>>> def combined_example(pos_only, /, standard, *, kwd_only):
... print(pos_only, standard, kwd_only)
The first function definition, standard_arg
, the most familiar form,
places no restrictions on the calling convention and arguments may be
passed by position or keyword:
>>> standard_arg(2)
2
>>> standard_arg(arg=2)
2
The second function pos_only_arg
is restricted to only use positional
parameters as there is a /
in the function definition:
>>> pos_only_arg(1)
1
>>> pos_only_arg(arg=1)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: pos_only_arg() got an unexpected keyword argument 'arg'
The third function kwd_only_args
only allows keyword arguments as indicated
by a *
in the function definition:
>>> kwd_only_arg(3)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: kwd_only_arg() takes 0 positional arguments but 1 was given
>>> kwd_only_arg(arg=3)
3
And the last uses all three calling conventions in the same function definition:
>>> combined_example(1, 2, 3)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: combined_example() takes 2 positional arguments but 3 were given
>>> combined_example(1, 2, kwd_only=3)
1 2 3
>>> combined_example(1, standard=2, kwd_only=3)
1 2 3
>>> combined_example(pos_only=1, standard=2, kwd_only=3)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: combined_example() got an unexpected keyword argument 'pos_only'
Finally, consider this function definition which has a potential collision between the positional argument name
and **kwds
which has name
as a key:
def foo(name, **kwds):
return 'name' in kwds
There is no possible call that will make it return True
as the keyword 'name'
will always to bind to the first parameter. For example:
>>> foo(1, **{'name': 2})
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: foo() got multiple values for argument 'name'
>>>
But using /
(positional only arguments), it is possible since it allows name
as a positional argument and 'name'
as a key in the keyword arguments:
def foo(name, /, **kwds):
return 'name' in kwds
>>> foo(1, **{'name': 2})
True
In other words, the names of positional-only parameters can be used in
**kwds
without ambiguity.
4.7.3.5. Recap¶
The use case will determine which parameters to use in the function definition:
def f(pos1, pos2, /, pos_or_kwd, *, kwd1, kwd2):
As guidance:
Use positional-only if you want the name of the parameters to not be available to the user. This is useful when parameter names have no real meaning, if you want to enforce the order of the arguments when the function is called or if you need to take some positional parameters and arbitrary keywords.
Use keyword-only when names have meaning and the function definition is more understandable by being explicit with names or you want to prevent users relying on the position of the argument being passed.
For an API, use positional-only to prevent prevent breaking API changes if the parameter's name is modified in the future.
4.7.4. Arbitrary Argument Lists¶
Finally, the least frequently used option is to specify that a function can be called with an arbitrary number of arguments. These arguments will be wrapped up in a tuple (see Tuples 和序列 (Sequences)). Before the variable number of arguments, zero or more normal arguments may occur.
def write_multiple_items(file, separator, *args):
file.write(separator.join(args))
Normally, these variadic
arguments will be last in the list of formal
parameters, because they scoop up all remaining input arguments that are
passed to the function. Any formal parameters which occur after the *args
parameter are 'keyword-only' arguments, meaning that they can only be used as
keywords rather than positional arguments.
>>> def concat(*args, sep="/"):
... return sep.join(args)
...
>>> concat("earth", "mars", "venus")
'earth/mars/venus'
>>> concat("earth", "mars", "venus", sep=".")
'earth.mars.venus'
4.7.5. Unpacking Argument Lists¶
The reverse situation occurs when the arguments are already in a list or tuple
but need to be unpacked for a function call requiring separate positional
arguments. For instance, the built-in range()
function expects separate
start and stop arguments. If they are not available separately, write the
function call with the *
-operator to unpack the arguments out of a list
or tuple:
>>> list(range(3, 6)) # normal call with separate arguments
[3, 4, 5]
>>> args = [3, 6]
>>> list(range(*args)) # call with arguments unpacked from a list
[3, 4, 5]
In the same fashion, dictionaries can deliver keyword arguments with the
**
-operator:
>>> def parrot(voltage, state='a stiff', action='voom'):
... print("-- This parrot wouldn't", action, end=' ')
... print("if you put", voltage, "volts through it.", end=' ')
... print("E's", state, "!")
...
>>> d = {"voltage": "four million", "state": "bleedin' demised", "action": "VOOM"}
>>> parrot(**d)
-- This parrot wouldn't VOOM if you put four million volts through it. E's bleedin' demised !
4.7.6. Lambda Expressions¶
Small anonymous functions can be created with the lambda
keyword.
This function returns the sum of its two arguments: lambda a, b: a+b
.
Lambda functions can be used wherever function objects are required. They are
syntactically restricted to a single expression. Semantically, they are just
syntactic sugar for a normal function definition. Like nested function
definitions, lambda functions can reference variables from the containing
scope:
>>> def make_incrementor(n):
... return lambda x: x + n
...
>>> f = make_incrementor(42)
>>> f(0)
42
>>> f(1)
43
The above example uses a lambda expression to return a function. Another use is to pass a small function as an argument:
>>> pairs = [(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')]
>>> pairs.sort(key=lambda pair: pair[1])
>>> pairs
[(4, 'four'), (1, 'one'), (3, 'three'), (2, 'two')]
4.7.7. 說明文件字串¶
Here are some conventions about the content and formatting of documentation strings.
The first line should always be a short, concise summary of the object's purpose. For brevity, it should not explicitly state the object's name or type, since these are available by other means (except if the name happens to be a verb describing a function's operation). This line should begin with a capital letter and end with a period.
If there are more lines in the documentation string, the second line should be blank, visually separating the summary from the rest of the description. The following lines should be one or more paragraphs describing the object's calling conventions, its side effects, etc.
The Python parser does not strip indentation from multi-line string literals in Python, so tools that process documentation have to strip indentation if desired. This is done using the following convention. The first non-blank line after the first line of the string determines the amount of indentation for the entire documentation string. (We can't use the first line since it is generally adjacent to the string's opening quotes so its indentation is not apparent in the string literal.) Whitespace "equivalent" to this indentation is then stripped from the start of all lines of the string. Lines that are indented less should not occur, but if they occur all their leading whitespace should be stripped. Equivalence of whitespace should be tested after expansion of tabs (to 8 spaces, normally).
Here is an example of a multi-line docstring:
>>> def my_function():
... """Do nothing, but document it.
...
... No, really, it doesn't do anything.
... """
... pass
...
>>> print(my_function.__doc__)
Do nothing, but document it.
No, really, it doesn't do anything.
4.7.8. Function Annotations¶
Function annotations are completely optional metadata information about the types used by user-defined functions (see PEP 3107 and PEP 484 for more information).
函数标注 以字典的形式存放在函数的 __annotations__
属性中,并且不会影响函数的任何其他部分。 形参标注的定义方式是在形参名称后加上冒号,后面跟一个表达式,该表达式会被求值为标注的值。 返回值标注的定义方式是加上一个组合符号 ->
,后面跟一个表达式,该标注位于形参列表和表示 def
语句结束的冒号之间。 下面的示例有一个位置参数,一个关键字参数以及返回值带有相应标注:
>>> def f(ham: str, eggs: str = 'eggs') -> str:
... print("Annotations:", f.__annotations__)
... print("Arguments:", ham, eggs)
... return ham + ' and ' + eggs
...
>>> f('spam')
Annotations: {'ham': <class 'str'>, 'return': <class 'str'>, 'eggs': <class 'str'>}
Arguments: spam eggs
'spam and eggs'
4.8. Intermezzo: Coding Style¶
Now that you are about to write longer, more complex pieces of Python, it is a good time to talk about coding style. Most languages can be written (or more concise, formatted) in different styles; some are more readable than others. Making it easy for others to read your code is always a good idea, and adopting a nice coding style helps tremendously for that.
For Python, PEP 8 has emerged as the style guide that most projects adhere to; it promotes a very readable and eye-pleasing coding style. Every Python developer should read it at some point; here are the most important points extracted for you:
Use 4-space indentation, and no tabs.
4 spaces are a good compromise between small indentation (allows greater nesting depth) and large indentation (easier to read). Tabs introduce confusion, and are best left out.
Wrap lines so that they don't exceed 79 characters.
This helps users with small displays and makes it possible to have several code files side-by-side on larger displays.
Use blank lines to separate functions and classes, and larger blocks of code inside functions.
When possible, put comments on a line of their own.
Use docstrings.
Use spaces around operators and after commas, but not directly inside bracketing constructs:
a = f(1, 2) + g(3, 4)
.Name your classes and functions consistently; the convention is to use
CamelCase
for classes andlower_case_with_underscores
for functions and methods. Always useself
as the name for the first method argument (see A First Look at Classes for more on classes and methods).Don't use fancy encodings if your code is meant to be used in international environments. Python's default, UTF-8, or even plain ASCII work best in any case.
Likewise, don't use non-ASCII characters in identifiers if there is only the slightest chance people speaking a different language will read or maintain the code.
註解
- 1
Actually, call by object reference would be a better description, since if a mutable object is passed, the caller will see any changes the callee makes to it (items inserted into a list).