U ovom uputstvu naučit ćemo pisati CSV datoteke s različitim formatima u Pythonu uz pomoć primjera.
csvZa ovaj ćemo zadatak koristiti isključivo modul ugrađen u Python. Ali prvo, morat ćemo uvesti modul kao:
import csv
Već smo pokrili osnove kako koristiti csvmodul za čitanje i pisanje u CSV datoteke. Ako nemate pojma o korištenju csvmodula, pogledajte naš vodič o Python CSV: Čitanje i pisanje CSV datoteka
Osnovna upotreba csv.writer ()
Pogledajmo osnovni primjer korištenja csv.writer()za osvježavanje postojećeg znanja.
Primjer 1: Zapišite u CSV datoteke pomoću csv.writer ()
Pretpostavimo da želimo napisati CSV datoteku sa sljedećim unosima:
SN, ime, doprinos 1, Linus Torvalds, Linux kernel 2, Tim Berners-Lee, World Wide Web 3, Guido van Rossum, programiranje na Pythonu
Evo kako to radimo.
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"))
Kada smo pokrenuti gore program, na innovators.csv datoteka stvorena u trenutni radni direktorij sa zadanim unosa.
Ovdje smo otvorili datoteku innovators.csv u načinu pisanja pomoću open()funkcije.
Da biste saznali više o otvaranju datoteka u Pythonu, posjetite: Ulaz / izlaz Python datoteke
Dalje, csv.writer()funkcija se koristi za stvaranje writerobjekta. writer.writerow()Funkcija se potom koristi za pisanje jednog reda na CSV datoteku.
Primjer 2: Zapisivanje više redaka s upisima ()
Ako moramo zapisati sadržaj dvodimenzionalnog popisa u CSV datoteku, evo kako to možemo učiniti.
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)
Rezultat programa je isti kao u primjeru 1 .
Ovdje se naš dvodimenzionalni popis prosljeđuje writer.writerows()funkciji za upisivanje sadržaja popisa u CSV datoteku.
Sada da vidimo kako možemo pisati CSV datoteke u različite formate. Zatim ćemo naučiti kako prilagoditi csv.writer()funkciju za njihovo pisanje.
CSV datoteke s prilagođenim graničnicima
Prema zadanim postavkama zarez se koristi kao graničnik u CSV datoteci. Međutim, neke CSV datoteke mogu koristiti graničnike koji nisu zarez. Malo je popularnih |i .
Pretpostavimo da želimo koristiti |kao graničnik u datoteci innovators.csv iz primjera 1 . Da bismo napisali ovu datoteku, funkciji možemo proslijediti dodatni delimiterparametar csv.writer().
Uzmimo primjer.
Primjer 3: Napišite CSV datoteku s razdjelnikom cijevi
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)
Izlaz
SN | Ime | Doprinos 1 | Linus Torvalds | Linux kernel 2 | Tim Berners-Lee | World Wide Web 3 | Guido van Rossum | Programiranje na Pythonu
Kao što vidimo, neobavezni parametar delimiter = '|'pomaže u specificiranju writerobjekta koji bi CSV datoteka trebala imati |kao graničnik.
CSV datoteke s navodnicima
Neke CSV datoteke imaju citate oko svakog ili nekih unosa.
Uzmimo za primjer quotes.csv sa sljedećim unosima:
"SN"; "Ime"; "Citati" 1; "Buddha"; "Ono što mislimo da smo postali" 2; "Mark Twain"; "Nikad ne žalite ni zbog čega što vam se nasmijalo" 3; "Oscar Wilde"; "Budi svoj svi ostali su zauzeti"
Korištenje csv.writer()prema zadanim postavkama neće dodati ove citate u stavke.
Da bismo ih dodali, morat ćemo upotrijebiti drugi opcijski parametar koji se naziva quoting.
Uzmimo primjer kako se citiranje može koristiti oko nenumeričkih vrijednosti i ;kao graničnici.
Primjer 4: Napišite CSV datoteke s navodnicima
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)
Izlaz
"SN"; "Ime"; "Citati" 1; "Buddha"; "Ono što mislimo da smo postali" 2; "Mark Twain"; "Nikad ne žalite ni zbog čega što vam se nasmijalo" 3; "Oscar Wilde"; "Budi svoj svi ostali su zauzeti"
Ovdje se datoteka quotes.csv kreira u radnom direktoriju s gore navedenim unosima.
Kao što vidite, prešli csv.QUOTE_NONNUMERICsmo na quotingparametar. To je konstanta koju definira csvmodul.
csv.QUOTE_NONNUMERICspecificira writerobjekt koji treba dodati u navodnike oko numeričkih unosa.
Postoje još 3 predefinirane konstante koje možete proslijediti quotingparametru:
csv.QUOTE_ALL- Određujewriterobjekt za pisanje CSV datoteke s navodnicima oko svih unosa.csv.QUOTE_MINIMAL- Određujewriterobjekt koji će navoditi samo ona polja koja sadrže posebne znakove ( graničnik , navodnik ili bilo koji znak u lineterminatoru )csv.QUOTE_NONE- Određujewriterobjekt za koji nijedan unos ne smije biti naveden. To je zadana vrijednost.
CSV datoteke s prilagođenim znakom citiranja
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 tofieldnames- alistobject 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.
Preporučeno čitanje: Pročitajte CSV datoteke na Pythonu
