14.1. csv --- Baca dan Tulis file CSV

Kode sumber: Lib/csv.py

Format CSV (Comma Separated Values) adalah format impor dan ekspor data yang paling umum digunakan untuk data spreadsheet dan database. Format CSV telah digunakan selama bertahun-tahun sebelum adanya upaya untuk mendeskripsikan format yang distandardisasi pada RFC 4180. Kurangnya standar yang terdefinisi dengan baik berarti banyak perbedaan tipis pada data yang dihasilkan dan digunakan dengan penggunaan yang berbeda. Perbedaan tersebut membuat tidak mudah untuk memproses file CSV dari beberapa sumber. Namun, meskipun karakter pembatas dan kutipan berbeda-beda, keseluruhan formatnya cukup mirip sehingga memungkinkan untuk menulis sebuah modul yang secara efisien dapat memanipulasi data tersebut.

Modul csv mengimplementasikan kelas-kelas untuk membaca dan menulis data tabular dengan format CSV. Hal ini memungkinkan pemrogram untuk mengatakan, "tulis data ini dalam format yang disukai oleh Excel," atau "baca data dari file ini yang dihasilkan oleh Excel," tanpa mengetahui detail persis dari format CSV yang digunakan oleh Excel. Pemrogram juga bisa mendeskripsikan format CSV yang dapat dipahami oleh aplikasi lain atau menentukan format CSV nya sendiri dengan tujuan tertentu.

Modul milik csv, reader dan writer objek membaca dan menulis urutan-urutan. Pemrogram juga bisa membaca dan menulis data dalam bentuk dictionary dengan menggunakan kelas DictReader dan DictWriter.

Lihat juga

PEP 305 - API File CSV

Python Enhancement Proposal (PEP) yang mengusulkan penambahan ini ke Python.

14.1.1. Modul-Modul

Modul csv memiliki fungsi-fungsi sebagai berikut:

csv.reader(csvfile, dialect='excel', **fmtparams)

Mengembalikan sebuah objek reader yang mengiterasikan baris baris pada csvfile yang diberikan. csvfile dapat berupa segala objek yang mendukung protokol iterator dan mengembalikan string setiap kali metode __next__() dipanggil --- objek file dan objek list keduanya cocok digunakan. Jika csvfile merupakan objek file, harus dibuka dengan newline=''. 1 Sebuah parameter dialek opsional dapat diberikan untuk mendefinisikan sebuah set parameter khusus untuk dialek CSV tertentu. Mungkin merupakan instansi sebuah subkelas dari kelas Dialect atau salah satu string yang dikembalikan oleh fungsi list_dialects(). Argumen kata kunci opsional fmtparams lainnya dapat diberikan untuk menimpa parameter-parameter pemformatan individu dalam dialek saat ini. Untuk detail lebih jelas mengenai dialek dan parameter format, lihat Dialek dan Parameter Pemformatan.

Setiap baris yang dibaca dari file csv dikembalikan sebagai list yang berisi strings. Tidak ada konversi tipe data secara otomatis dilakukan kecuali kalau opsi format QUOTE_NONNUMERIC ditentukan (dalam hal ini, bidang tanpa tanda kutip diubah menjadi bertipe floats).

Contoh penggunaan singkat:

>>> import csv
>>> with open('eggs.csv', newline='') as csvfile:
...     spamreader = csv.reader(csvfile, delimiter=' ', quotechar='|')
...     for row in spamreader:
...         print(', '.join(row))
Spam, Spam, Spam, Spam, Spam, Baked Beans
Spam, Lovely Spam, Wonderful Spam
csv.writer(csvfile, dialect='excel', **fmtparams)

Return a writer object responsible for converting the user's data into delimited strings on the given file-like object. csvfile can be any object with a write() method. If csvfile is a file object, it should be opened with newline='' 1. An optional dialect parameter can be given which is used to define a set of parameters specific to a particular CSV dialect. It may be an instance of a subclass of the Dialect class or one of the strings returned by the list_dialects() function. The other optional fmtparams keyword arguments can be given to override individual formatting parameters in the current dialect. For full details about the dialect and formatting parameters, see section Dialek dan Parameter Pemformatan. To make it as easy as possible to interface with modules which implement the DB API, the value None is written as the empty string. While this isn't a reversible transformation, it makes it easier to dump SQL NULL data values to CSV files without preprocessing the data returned from a cursor.fetch* call. All other non-string data are stringified with str() before being written.

Contoh penggunaan singkat:

import csv
with open('eggs.csv', 'w', newline='') as csvfile:
    spamwriter = csv.writer(csvfile, delimiter=' ',
                            quotechar='|', quoting=csv.QUOTE_MINIMAL)
    spamwriter.writerow(['Spam'] * 5 + ['Baked Beans'])
    spamwriter.writerow(['Spam', 'Lovely Spam', 'Wonderful Spam'])
csv.register_dialect(name[, dialect[, **fmtparams]])

Associate dialect with name. name must be a string. The dialect can be specified either by passing a sub-class of Dialect, or by fmtparams keyword arguments, or both, with keyword arguments overriding parameters of the dialect. For full details about the dialect and formatting parameters, see section Dialek dan Parameter Pemformatan.

csv.unregister_dialect(name)

Delete the dialect associated with name from the dialect registry. An Error is raised if name is not a registered dialect name.

csv.get_dialect(name)

Return the dialect associated with name. An Error is raised if name is not a registered dialect name. This function returns an immutable Dialect.

csv.list_dialects()

Mengembalikan nama dari semua dialek yang terdaftar.

csv.field_size_limit([new_limit])

Mengembalikan nilai maksimum ukuran field yang diperbolekan saat ini oleh parser. Jika new_limit diberikan, hal tersebut menjadi limit baru.

Modul csv berisi kelas-kelas dibawah ini:

class csv.DictReader(f, fieldnames=None, restkey=None, restval=None, dialect='excel', *args, **kwds)

Create an object that operates like a regular reader but maps the information in each row to an OrderedDict whose keys are given by the optional fieldnames parameter.

The fieldnames parameter is a sequence. If fieldnames is omitted, the values in the first row of file f will be used as the fieldnames. Regardless of how the fieldnames are determined, the ordered dictionary preserves their original ordering.

If a row has more fields than fieldnames, the remaining data is put in a list and stored with the fieldname specified by restkey (which defaults to None). If a non-blank row has fewer fields than fieldnames, the missing values are filled-in with None.

All other optional or keyword arguments are passed to the underlying reader instance.

Berubah pada versi 3.6: Baris-baris yang dikembalikan sekarang memiliki tipe OrderedDict.

Contoh penggunaan singkat:

>>> import csv
>>> with open('names.csv', newline='') as csvfile:
...     reader = csv.DictReader(csvfile)
...     for row in reader:
...         print(row['first_name'], row['last_name'])
...
Eric Idle
John Cleese

>>> print(row)
OrderedDict([('first_name', 'John'), ('last_name', 'Cleese')])
class csv.DictWriter(f, fieldnames, restval='', extrasaction='raise', dialect='excel', *args, **kwds)

Create an object which operates like a regular writer but maps dictionaries onto output rows. The fieldnames parameter is a sequence of keys that identify the order in which values in the dictionary passed to the writerow() method are written to file f. The optional restval parameter specifies the value to be written if the dictionary is missing a key in fieldnames. If the dictionary passed to the writerow() method contains a key not found in fieldnames, the optional extrasaction parameter indicates what action to take. If it is set to 'raise', the default value, a ValueError is raised. If it is set to 'ignore', extra values in the dictionary are ignored. Any other optional or keyword arguments are passed to the underlying writer instance.

Note that unlike the DictReader class, the fieldnames parameter of the DictWriter is not optional. Since Python's dict objects are not ordered, there is not enough information available to deduce the order in which the row should be written to file f.

Contoh penggunaan singkat:

import csv

with open('names.csv', 'w', newline='') as csvfile:
    fieldnames = ['first_name', 'last_name']
    writer = csv.DictWriter(csvfile, fieldnames=fieldnames)

    writer.writeheader()
    writer.writerow({'first_name': 'Baked', 'last_name': 'Beans'})
    writer.writerow({'first_name': 'Lovely', 'last_name': 'Spam'})
    writer.writerow({'first_name': 'Wonderful', 'last_name': 'Spam'})
class csv.Dialect

The Dialect class is a container class relied on primarily for its attributes, which are used to define the parameters for a specific reader or writer instance.

class csv.excel

The excel class defines the usual properties of an Excel-generated CSV file. It is registered with the dialect name 'excel'.

class csv.excel_tab

The excel_tab class defines the usual properties of an Excel-generated TAB-delimited file. It is registered with the dialect name 'excel-tab'.

class csv.unix_dialect

The unix_dialect class defines the usual properties of a CSV file generated on UNIX systems, i.e. using '\n' as line terminator and quoting all fields. It is registered with the dialect name 'unix'.

Baru pada versi 3.2.

class csv.Sniffer

Kelas Sniffer digunakan untuk menyimpulkan format sebuah file CSV.

Kelas Sniffer menyediakan dua metode:

sniff(sample, delimiters=None)

Analyze the given sample and return a Dialect subclass reflecting the parameters found. If the optional delimiters parameter is given, it is interpreted as a string containing possible valid delimiter characters.

has_header(sample)

Analyze the sample text (presumed to be in CSV format) and return True if the first row appears to be a series of column headers.

Sebuah contoh untuk penggunaan Sniffer:

with open('example.csv', newline='') as csvfile:
    dialect = csv.Sniffer().sniff(csvfile.read(1024))
    csvfile.seek(0)
    reader = csv.reader(csvfile, dialect)
    # ... process CSV file contents here ...

The csv module defines the following constants:

csv.QUOTE_ALL

Menginstruksikan objek writer untuk mengutip semua fields.

csv.QUOTE_MINIMAL

Menginstruksikan objek writer untuk hanya mengutip fields yang berisi karakter spesial seperti delimiter, quotechar atau salah satu karakter dalam lineterminator.

csv.QUOTE_NONNUMERIC

Menginstuksikan objek writer untuk mengutip semua fields yang tidak memiliki angka.

Mengisntruksikan reader untuk mengonversi semua fields yang tidak dikutip menjadi tipe float.

csv.QUOTE_NONE

Instructs writer objects to never quote fields. When the current delimiter occurs in output data it is preceded by the current escapechar character. If escapechar is not set, the writer will raise Error if any characters that require escaping are encountered.

Menginstruksikan reader untuk tidak melakukan pemrosesan khusus terhadap karakter kutipan

Modul csv berisi exception dibawah ini:

exception csv.Error

Raised by any of the functions when an error is detected.

14.1.2. Dialek dan Parameter Pemformatan

To make it easier to specify the format of input and output records, specific formatting parameters are grouped together into dialects. A dialect is a subclass of the Dialect class having a set of specific methods and a single validate() method. When creating reader or writer objects, the programmer can specify a string or a subclass of the Dialect class as the dialect parameter. In addition to, or instead of, the dialect parameter, the programmer can also specify individual formatting parameters, which have the same names as the attributes defined below for the Dialect class.

Dialek mendukung atribut dibawah ini:

Dialect.delimiter

Sebuah karakter yang digunakan sebagai pemisah fields. Dengan nilai bawaan ','.

Dialect.doublequote

Controls how instances of quotechar appearing inside a field should themselves be quoted. When True, the character is doubled. When False, the escapechar is used as a prefix to the quotechar. It defaults to True.

On output, if doublequote is False and no escapechar is set, Error is raised if a quotechar is found in a field.

Dialect.escapechar

A one-character string used by the writer to escape the delimiter if quoting is set to QUOTE_NONE and the quotechar if doublequote is False. On reading, the escapechar removes any special meaning from the following character. It defaults to None, which disables escaping.

Dialect.lineterminator

The string used to terminate lines produced by the writer. It defaults to '\r\n'.

Catatan

The reader is hard-coded to recognise either '\r' or '\n' as end-of-line, and ignores lineterminator. This behavior may change in the future.

Dialect.quotechar

A one-character string used to quote fields containing special characters, such as the delimiter or quotechar, or which contain new-line characters. It defaults to '"'.

Dialect.quoting

Controls when quotes should be generated by the writer and recognised by the reader. It can take on any of the QUOTE_* constants (see section Modul-Modul) and defaults to QUOTE_MINIMAL.

Dialect.skipinitialspace

When True, whitespace immediately following the delimiter is ignored. The default is False.

Dialect.strict

When True, raise exception Error on bad CSV input. The default is False.

14.1.3. Reader Objects

Reader objects (DictReader instances and objects returned by the reader() function) have the following public methods:

csvreader.__next__()

Return the next row of the reader's iterable object as a list (if the object was returned from reader()) or a dict (if it is a DictReader instance), parsed according to the current dialect. Usually you should call this as next(reader).

Reader objects have the following public attributes:

csvreader.dialect

A read-only description of the dialect in use by the parser.

csvreader.line_num

The number of lines read from the source iterator. This is not the same as the number of records returned, as records can span multiple lines.

Objek DictReader memiliki atribut publik sebagai berikut:

csvreader.fieldnames

If not passed as a parameter when creating the object, this attribute is initialized upon first access or when the first record is read from the file.

14.1.4. Writer Objects

Writer objects (DictWriter instances and objects returned by the writer() function) have the following public methods. A row must be an iterable of strings or numbers for Writer objects and a dictionary mapping fieldnames to strings or numbers (by passing them through str() first) for DictWriter objects. Note that complex numbers are written out surrounded by parens. This may cause some problems for other programs which read CSV files (assuming they support complex numbers at all).

csvwriter.writerow(row)

Write the row parameter to the writer's file object, formatted according to the current dialect.

Berubah pada versi 3.5: Added support of arbitrary iterables.

csvwriter.writerows(rows)

Write all elements in rows (an iterable of row objects as described above) to the writer's file object, formatted according to the current dialect.

Writer objects have the following public attribute:

csvwriter.dialect

A read-only description of the dialect in use by the writer.

Objek DictWriter memiliki metode publik sebagai berikut:

DictWriter.writeheader()

Write a row with the field names (as specified in the constructor).

Baru pada versi 3.2.

14.1.5. Contoh-contoh

Contoh paling sederhana dari membaca sebuah file CSV:

import csv
with open('some.csv', newline='') as f:
    reader = csv.reader(f)
    for row in reader:
        print(row)

Membaca file dengan format lain:

import csv
with open('passwd', newline='') as f:
    reader = csv.reader(f, delimiter=':', quoting=csv.QUOTE_NONE)
    for row in reader:
        print(row)

Contoh paling sederhana dari menulis ke sebuah file CSV:

import csv
with open('some.csv', 'w', newline='') as f:
    writer = csv.writer(f)
    writer.writerows(someiterable)

Karena open() digunakan untuk membaca file CSV, file secara default akan diterjemahkan menjadi unicode menggunakan default encoding dari sistem (lihat locale.getpreferredencoding()). Untuk menerjemahkan sebuah file dengan encoding yang berbeda, gunakan argumen encoding pada open():

import csv
with open('some.csv', newline='', encoding='utf-8') as f:
    reader = csv.reader(f)
    for row in reader:
        print(row)

Hal yang sama berlaku ketika menulis sesuatu yang berbeda dengan default encoding dari sistem: tentukan argumen encoding ketika membuka file output.

Mendaftarkan dialek baru:

import csv
csv.register_dialect('unixpwd', delimiter=':', quoting=csv.QUOTE_NONE)
with open('passwd', newline='') as f:
    reader = csv.reader(f, 'unixpwd')

A slightly more advanced use of the reader --- catching and reporting errors:

import csv, sys
filename = 'some.csv'
with open(filename, newline='') as f:
    reader = csv.reader(f)
    try:
        for row in reader:
            print(row)
    except csv.Error as e:
        sys.exit('file {}, line {}: {}'.format(filename, reader.line_num, e))

And while the module doesn't directly support parsing strings, it can easily be done:

import csv
for row in csv.reader(['one,two,three']):
    print(row)

Catatan kaki

1(1,2)

If newline='' is not specified, newlines embedded inside quoted fields will not be interpreted correctly, and on platforms that use \r\n linendings on write an extra \r will be added. It should always be safe to specify newline='', since the csv module does its own (universal) newline handling.