V tej vadnici se bomo s pomočjo primerov naučili pisati datoteke CSV z različnimi formati v Pythonu.
Za csvto nalogo bomo uporabili izključno modul, vgrajen v Python. Najprej pa bomo morali modul uvoziti kot:
import csv
Osnove uporabe csvmodula za branje in pisanje v datoteke CSV smo že zajeli . Če nimate pojma o uporabi csvmodula, si oglejte našo vadnico o Python CSV: branje in pisanje datotek CSV
Osnovna uporaba csv.writer ()
Oglejmo si osnovni primer uporabe csv.writer()za osvežitev obstoječega znanja.
Primer 1: Zapišite v datoteke CSV s csv.writer ()
Recimo, da želimo napisati datoteko CSV z naslednjimi vnosi:
SN, Ime, Prispevek 1, Linus Torvalds, Linux Kernel 2, Tim Berners-Lee, World Wide Web 3, Guido van Rossum, Python Programming
Evo, kako to storimo.
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"))
Ko zaženemo zgornji program, se v trenutnem delovnem imeniku z danimi vnosi ustvari datoteka innovators.csv .
Tukaj smo datoteko innovators.csv odprli v načinu pisanja s pomočjo open()funkcije.
Če želite izvedeti več o odpiranju datotek v Pythonu, obiščite: Vnos / izhod datotek Python
Nato se csv.writer()funkcija uporablja za ustvarjanje writerpredmeta. Nato se writer.writerow()funkcija uporablja za zapisovanje posameznih vrstic v datoteko CSV.
Primer 2: Zapisovanje več vrstic s pisalnimi črkami ()
Če moramo vsebino dvodimenzionalnega seznama zapisati v datoteko CSV, lahko to storimo tako.
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 enak kot v primeru 1 .
Tu se naš dvodimenzionalni seznam posreduje writer.writerows()funkciji za zapis vsebine seznama v datoteko CSV.
Zdaj pa poglejmo, kako lahko zapisujemo datoteke CSV v različnih oblikah. Nato se bomo naučili, kako prilagoditi csv.writer()funkcijo, da jih zapišemo.
Datoteke CSV z ločevalniki po meri
Privzeto se vejica uporablja kot ločilo v datoteki CSV. Vendar lahko nekatere datoteke CSV uporabljajo ločila, ki niso vejica. Nekaj priljubljenih je |in .
Recimo, da želimo uporabiti |ločilo v datoteki innovators.csv iz primera 1 . Za pisanje te datoteke lahko funkciji posredujemo dodaten delimiterparameter csv.writer().
Vzemimo primer.
Primer 3: Napišite datoteko CSV z ločevalnikom cevi
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)
Izhod
SN | Ime | Prispevek 1 | Linus Torvalds | Linux Kernel 2 | Tim Berners-Lee | Svetovni splet 3 | Guido van Rossum | Programiranje na Python
Kot lahko vidimo, neobvezni parameter delimiter = '|'pomaga določiti writerpredmet, ki ga mora imeti datoteka CSV |kot ločilo.
Datoteke CSV z narekovaji
Nekatere datoteke CSV imajo citate okoli vsakega ali nekaterih vnosov.
Za primer vzemimo quotes.csv z naslednjimi vnosi:
"SN"; "Ime"; "Citati" 1; "Buda"; "Kaj mislimo, da postanemo" 2; "Mark Twain"; "Nikoli ne obžalujte ničesar, kar vas je nasmejalo" 3; "Oscar Wilde"; "Bodite sami vsi ostali so že zajeti "
csv.writer()Privzeta uporaba teh navednic ne bo dodala vnosom.
Če jih želimo dodati, bomo morali uporabiti drug imenovani neobvezni parameter quoting.
Vzemimo primer, kako lahko citiranje uporabimo okoli neštevilskih vrednosti in ;kot ločila.
4. primer: Datoteke CSV napišite z narekovaji
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)
Izhod
"SN"; "Ime"; "Citati" 1; "Buda"; "Kaj mislimo, da postanemo" 2; "Mark Twain"; "Nikoli ne obžalujte ničesar, kar vas je nasmejalo" 3; "Oscar Wilde"; "Bodite sami vsi ostali so že zajeti "
Tu je datoteka quotes.csv ustvarjena v delovnem imeniku z zgornjimi vnosi.
Kot lahko vidite, smo prešli csv.QUOTE_NONNUMERICna quotingparameter. To je konstanta, ki jo določa csvmodul.
csv.QUOTE_NONNUMERICdoloča writerobjekt, ki ga je treba dodati narekovaje okrog neštevilskih vnosov.
quotingParametru lahko posredujete še 3 vnaprej določene konstante :
csv.QUOTE_ALL- Določawriterobjekt za zapisovanje datoteke CSV z narekovaji okoli vseh vnosov.csv.QUOTE_MINIMAL- Določawriterobjekt, da navede le tista polja, ki vsebujejo posebne znake ( ločilo , narekovaj ali kateri koli znak v določitelju vrstic )csv.QUOTE_NONE- Določawriterobjekt, pri katerem noben vnos ne sme biti naveden. To je privzeta vrednost.
Datoteke CSV z znakom za navajanje po meri
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.
Priporočeno branje: Preberite datoteke CSV v Pythonu
