CSV failų rašymas „Python“

Šioje pamokoje išmoksime rašyti skirtingų formatų CSV failus „Python“ pavyzdžių pagalba.

csvŠiai užduočiai ketiname naudoti tik „ Python“ integruotą modulį. Bet pirmiausia turėsime importuoti modulį kaip:

 import csv 

Mes jau apžvelgėme pagrindus, kaip naudoti csvmodulį skaityti ir rašyti į CSV failus. Jei neturite idėjos naudoti csvmodulį, peržiūrėkite mūsų „Python CSV“ pamoką: skaitykite ir rašykite CSV failus

Pagrindinis „csv.writer“ () naudojimas

Pažvelkime į pagrindinį pavyzdį, csv.writer()kaip atnaujinti turimas žinias.

1 pavyzdys: įrašykite į CSV failus naudodami csv.writer ()

Tarkime, kad mes norime parašyti CSV failą su šiais įrašais:

 SN, vardas, 1 indėlis, Linusas Torvaldsas, „Linux“ branduolys 2, Timas Bernersas-Lee, „World Wide Web 3“, Guido van Rossum, „Python“ programavimas 

Štai kaip mes tai darome.

 import csv with open('innovators.csv', 'w', newline='') as file: writer = csv.writer(file) writer.writerow(("SN", "Name", "Contribution")) writer.writerow((1, "Linus Torvalds", "Linux Kernel")) writer.writerow((2, "Tim Berners-Lee", "World Wide Web")) writer.writerow((3, "Guido van Rossum", "Python Programming")) 

Paleidus aukščiau nurodytą programą, dabartiniame darbo kataloge su pateiktais įrašais sukuriamas failas „ innovators.csv“ .

Čia atidarėme failą „ innovators.csv “ rašymo režimu, naudodami open()funkciją.

Norėdami sužinoti daugiau apie failų atidarymą „Python“, apsilankykite: „Python“ failų įvestis / išvestis

Tada csv.writer()funkcija naudojama kuriant writerobjektą. Tada writer.writerow()funkcija naudojama atskiroms eilutėms įrašyti į CSV failą.

2 pavyzdys: kelių eilučių rašymas naudojant rašytojo eilutes ()

Jei mums reikia parašyti dviejų matmenų sąrašo turinį į CSV failą, štai kaip tai padaryti.

 import csv row_list = (("SN", "Name", "Contribution"), (1, "Linus Torvalds", "Linux Kernel"), (2, "Tim Berners-Lee", "World Wide Web"), (3, "Guido van Rossum", "Python Programming")) with open('protagonist.csv', 'w', newline='') as file: writer = csv.writer(file) writer.writerows(row_list) 

Programos išvestis yra tokia pati kaip 1 pavyzdyje .

Čia mūsų dviejų matmenų sąrašas perduodamas writer.writerows()funkcijai, kad sąrašo turinys būtų įrašytas į CSV failą.

Dabar pažiūrėkime, kaip mes galime parašyti CSV failus įvairiais formatais. Tada mes sužinosime, kaip pritaikyti csv.writer()funkciją, kad juos parašytume.

CSV failai su pasirinktais atribotais

Pagal numatytuosius nustatymus kablelis naudojamas kaip atskyriklis CSV faile. Tačiau kai kuriuose CSV failuose skiriamieji skirikliai gali būti naudojami ne kableliu. Nedaugelis populiarių yra |ir .

Tarkime, kad norime naudoti |kaip atskyriklį 1 pavyzdžio faile „ innovators.csv“ . Norėdami parašyti šį failą, galime perduoti papildomą parametrą funkcijai.delimitercsv.writer()

Paimkime pavyzdį.

3 pavyzdys: CSV failo rašymas turint vamzdžių ribotuvą

 import csv data_list = (("SN", "Name", "Contribution"), (1, "Linus Torvalds", "Linux Kernel"), (2, "Tim Berners-Lee", "World Wide Web"), (3, "Guido van Rossum", "Python Programming")) with open('innovators.csv', 'w', newline='') as file: writer = csv.writer(file, delimiter='|') writer.writerows(data_list) 

Rezultatas

 SN | Vardas | Indėlis 1 | Linus Torvalds | Linux Kernel 2 | Tim Berners-Lee | 3 pasaulinis internetas | Guido van Rossum | „Python“ programavimas 

Kaip matome, pasirenkamas parametras delimiter = '|'padeda nurodyti writerobjektą, kurį CSV failas turėtų turėti |kaip atskirtį.

CSV failai su citatomis

Kai kurie CSV failai turi kabutes prie kiekvieno ar kai kurių įrašų.

Paimkime pavyzdį quotes.csv su šiais įrašais:

 „SN“; „Vardas“; „Citatos“ 1; „Buda“; „Tai, kuo mes manome, kad tampame„ 2; „Markas Tvenas“; „Niekada nesigailėkite dėl nieko, kas privertė jus šypsotis“ 3; „Oskaras Vaildas“; „Būk savimi“ Visi kiti jau užimti" 

Naudojant csv.writer()pagal numatytuosius nustatymus šios citatos prie įrašų nebus pridėtos.

Norėdami juos pridėti, turėsime naudoti kitą pasirinktinį parametrą, vadinamą quoting.

Paimkime pavyzdį, kaip citatos gali būti naudojamos ne skaitinėms vertėms ir ;kaip atribotojams.

4 pavyzdys: rašykite CSV failus su kabutėmis

 import csv row_list = ( ("SN", "Name", "Quotes"), (1, "Buddha", "What we think we become"), (2, "Mark Twain", "Never regret anything that made you smile"), (3, "Oscar Wilde", "Be yourself everyone else is already taken") ) with open('quotes.csv', 'w', newline='') as file: writer = csv.writer(file, quoting=csv.QUOTE_NONNUMERIC, delimiter=';') writer.writerows(row_list) 

Rezultatas

 „SN“; „Vardas“; „Citatos“ 1; „Buda“; „Tai, kuo mes manome, kad tampame„ 2; „Markas Tvenas“; „Niekada nesigailėkite dėl nieko, kas privertė jus šypsotis“ 3; „Oskaras Vaildas“; „Būk savimi“ Visi kiti jau užimti" 

Čia darbo kataloge sukuriamas failas quotes.csv su aukščiau nurodytais įrašais.

Kaip matote, mes perėjome csv.QUOTE_NONNUMERICprie quotingparametro. Tai csvmodulio apibrėžta konstanta .

csv.QUOTE_NONNUMERICnurodo writerobjektą, kurį kabutės turėtų būti pridėtos prie skaitmenų įrašų.

quotingParametrui galite perduoti dar 3 iš anksto nustatytas konstantas :

• csv.QUOTE_ALL- Nurodo writerobjektą, kuriuo reikia rašyti CSV failą su kabutėmis aplink visus įrašus.
• csv.QUOTE_MINIMAL- Nurodo writerobjektą, kuris cituoja tik tuos laukus, kuriuose yra specialiųjų simbolių ( ribotuvas , kabutė ar bet kokie simboliai lineterminatoriuje )
• csv.QUOTE_NONE- Nurodo writerobjektą, kurio nė vienas įrašas neturėtų būti cituojamas. Tai yra numatytoji reikšmė.

CSV failai su pasirinktu cituojančiu simboliu

We can also write CSV files with custom quoting characters. For that, we will have to use an optional parameter called quotechar.

Let's take an example of writing quotes.csv file in Example 4, but with * as the quoting character.

Example 5: Writing CSV files with custom quoting character

 import csv row_list = ( ("SN", "Name", "Quotes"), (1, "Buddha", "What we think we become"), (2, "Mark Twain", "Never regret anything that made you smile"), (3, "Oscar Wilde", "Be yourself everyone else is already taken") ) with open('quotes.csv', 'w', newline='') as file: writer = csv.writer(file, quoting=csv.QUOTE_NONNUMERIC, delimiter=';', quotechar='*') writer.writerows(row_list) 

Output

 *SN*;*Name*;*Quotes* 1;*Buddha*;*What we think we become* 2;*Mark Twain*;*Never regret anything that made you smile* 3;*Oscar Wilde*;*Be yourself everyone else is already taken* 

Here, we can see that quotechar='*' parameter instructs the writer object to use * as quote for all non-numeric values.

Dialects in CSV module

Notice in Example 5 that we have passed multiple parameters (quoting, delimiter and quotechar) to the csv.writer() function.

This practice is acceptable when dealing with one or two files. But it will make the code more redundant and ugly once we start working with multiple CSV files with similar formats.

As a solution to this, the csv module offers dialect as an optional parameter.

Dialect helps in grouping together many specific formatting patterns like delimiter, skipinitialspace, quoting, escapechar into a single dialect name.

It can then be passed as a parameter to multiple writer or reader instances.

Example 6: Write CSV file using dialect

Suppose we want to write a CSV file (office.csv) with the following content:

 "ID"|"Name"|"Email" "A878"|"Alfonso K. Hamby"|"[email protected]" "F854"|"Susanne Briard"|"[email protected]" "E833"|"Katja Mauer"|"[email protected]" 

The CSV file has quotes around each entry and uses | as a delimiter.

Instead of passing two individual formatting patterns, let's look at how to use dialects to write this file.

 import csv row_list = ( ("ID", "Name", "Email"), ("A878", "Alfonso K. Hamby", "[email protected]"), ("F854", "Susanne Briard", "[email protected]"), ("E833", "Katja Mauer", "[email protected]") ) csv.register_dialect('myDialect', delimiter='|', quoting=csv.QUOTE_ALL) with open('office.csv', 'w', newline='') as file: writer = csv.writer(file, dialect='myDialect') writer.writerows(row_list) 

Output

 "ID"|"Name"|"Email" "A878"|"Alfonso K. Hamby"|"[email protected]" "F854"|"Susanne Briard"|"[email protected]" "E833"|"Katja Mauer"|"[email protected]" 

Here, office.csv is created in the working directory with the above contents.

From this example, we can see that the csv.register_dialect() function is used to define a custom dialect. Its syntax is:

 csv.register_dialect(name(, dialect(, **fmtparams))) 

The custom dialect requires a name in the form of a string. Other specifications can be done either by passing a sub-class of the Dialect class, or by individual formatting patterns as shown in the example.

While creating the writer object, we pass dialect='myDialect' to specify that the writer instance must use that particular dialect.

The advantage of using dialect is that it makes the program more modular. Notice that we can reuse myDialect to write other CSV files without having to re-specify the CSV format.

Write CSV files with csv.DictWriter()

The objects of csv.DictWriter() class can be used to write to a CSV file from a Python dictionary.

The minimal syntax of the csv.DictWriter() class is:

 csv.DictWriter(file, fieldnames) 

Here,

• file - CSV file where we want to write to
• fieldnames - a list object which should contain the column headers specifying the order in which data should be written in the CSV file

Example 7: Python csv.DictWriter()

 import csv with open('players.csv', 'w', newline='') as file: fieldnames = ('player_name', 'fide_rating') writer = csv.DictWriter(file, fieldnames=fieldnames) writer.writeheader() writer.writerow(('player_name': 'Magnus Carlsen', 'fide_rating': 2870)) writer.writerow(('player_name': 'Fabiano Caruana', 'fide_rating': 2822)) writer.writerow(('player_name': 'Ding Liren', 'fide_rating': 2801)) 

Output

The program creates a players.csv file with the following entries:

 player_name,fide_rating Magnus Carlsen,2870 Fabiano Caruana,2822 Ding Liren,2801 

The full syntax of the csv.DictWriter() class is:

 csv.DictWriter(f, fieldnames, restval='', extrasaction='raise', dialect='excel', *args, **kwds) 

To learn more about it in detail, visit: Python csv.DictWriter() class

CSV files with lineterminator

A lineterminator is a string used to terminate lines produced by writer objects. The default value is . You can change its value by passing any string as a lineterminator parameter.

However, the reader object only recognizes or as lineterminator values. So using other characters as line terminators is highly discouraged.

doublequote & escapechar in CSV module

In order to separate delimiter characters in the entries, the csv module by default quotes the entries using quotation marks.

So, if you had an entry: He is a strong, healthy man, it will be written as: "He is a strong, healthy man".

Similarly, the csv module uses double quotes in order to escape the quote character present in the entries by default.

If you had an entry: Go to "programiz.com", it would be written as: "Go to ""programiz.com""".

Here, we can see that each " is followed by a " to escape the previous one.

doublequote

It handles how quotechar present in the entry themselves are quoted. When True, the quoting character is doubled and when False, the escapechar is used as a prefix to the quotechar. By default its value is True.

escapechar

escapechar parameter is a string to escape the delimiter if quoting is set to csv.QUOTE_NONE and quotechar if doublequote is False. Its default value is None.

Example 8: Using escapechar in csv writer

 import csv row_list = ( ('Book', 'Quote'), ('Lord of the Rings', '"All we have to decide is what to do with the time that is given us."'), ('Harry Potter', '"It matters not what someone is born, but what they grow to be."') ) with open('book.csv', 'w', newline='') as file: writer = csv.writer(file, escapechar='/', quoting=csv.QUOTE_NONE) writer.writerows(row_list) 

Output

 Book,Quote Lord of the Rings,/"All we have to decide is what to do with the time that is given us./" Harry Potter,/"It matters not what someone is born/, but what they grow to be./" 

Here, we can see that / is prefix to all the " and , because we specified quoting=csv.QUOTE_NONE.

If it wasn't defined, then, the output would be:

 Book,Quote Lord of the Rings,"""All we have to decide is what to do with the time that is given us.""" Harry Potter,"""It matters not what someone is born, but what they grow to be.""" 

Since we allow quoting, the entries with special characters(" in this case) are double-quoted. The entries with delimiter are also enclosed within quote characters.(Starting and closing quote characters)

The remaining quote characters are to escape the actual " present as part of the string, so that they are not interpreted as quotechar.

Note: The csv module can also be used for other file extensions (like: .txt) as long as their contents are in proper structure.

Rekomenduojamas skaitymas: skaitykite CSV failus „Python“