I den här handledningen lär vi oss att skriva CSV-filer med olika format i Python med hjälp av exempel.
Vi ska exklusivt använda den csvinbyggda modulen i Python för denna uppgift. Men först måste vi importera modulen som:
import csv
Vi har redan täckt grunderna för hur man använder csvmodulen för att läsa och skriva till CSV-filer. Om du inte har någon aning om att använda csvmodulen, kolla in vår handledning om Python CSV: Läs och skriv CSV-filer
Grundläggande användning av csv.writer ()
Låt oss titta på ett grundläggande exempel på att använda för csv.writer()att uppdatera din befintliga kunskap.
Exempel 1: Skriv till CSV-filer med csv.writer ()
Antag att vi vill skriva en CSV-fil med följande poster:
SN, Name, Contribution 1, Linus Torvalds, Linux Kernel 2, Tim Berners-Lee, World Wide Web 3, Guido van Rossum, Python Programming
Så här gör vi det.
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"))
När vi kör ovanstående program skapas en innovators.csv- fil i den aktuella arbetskatalogen med angivna poster.
Här har vi öppnat filen innovators.csv i skrivläge med open()funktionen.
För att lära dig mer om att öppna filer i Python, besök: Python File Input / Output
Därefter används csv.writer()funktionen för att skapa ett writerobjekt. Den writer.writerow()funktionen används sedan för att skriva enkla rader till CSV-filen.
Exempel 2: Skriva flera rader medwrows ()
Om vi behöver skriva innehållet i den tvådimensionella listan till en CSV-fil, så här kan vi göra det.
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)
Programmets utdata är densamma som i exempel 1 .
Här skickas vår tvådimensionella lista till writer.writerows()funktionen för att skriva innehållet i listan till CSV-filen.
Låt oss nu se hur vi kan skriva CSV-filer i olika format. Vi lär oss sedan hur man anpassar csv.writer()funktionen för att skriva dem.
CSV-filer med anpassade avgränsare
Som standard används ett komma som avgränsare i en CSV-fil. Vissa CSV-filer kan dock använda andra avgränsare än kommatecken. Få populära är |och .
Antag att vi vill använda |som en avgränsare i filen innovators.csv i exempel 1 . För att skriva den här filen kan vi skicka en ytterligare delimiterparameter till csv.writer()funktionen.
Låt oss ta ett exempel.
Exempel 3: Skriv CSV-fil med röravgränsare
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)
Produktion
SN | Namn | Bidrag 1 | Linus Torvalds | Linux Kernel 2 | Tim Berners-Lee | World Wide Web 3 | Guido van Rossum | Python Programming
Som vi kan se delimiter = '|'hjälper den valfria parametern att specificera det writerobjekt som CSV-filen ska ha |som avgränsare.
CSV-filer med offert
Vissa CSV-filer har citat runt var och en av posterna.
Låt oss ta citat.csv som ett exempel, med följande poster:
"SN"; "Namn"; "Citat" 1; "Buddha"; "Vad vi tror att vi blir" 2; "Mark Twain"; "Ångrar aldrig något som fick dig att le" 3; "Oscar Wilde"; "Var dig själv Alla andra är redan tagna"
Att använda som csv.writer()standard kommer inte att lägga till dessa citat i posterna.
För att lägga till dem måste vi använda en annan valfri parameter som heter quoting.
Låt oss ta ett exempel på hur citering kan användas runt icke-numeriska värden och ;som avgränsare.
Exempel 4: Skriv CSV-filer med citat
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)
Produktion
"SN"; "Namn"; "Citat" 1; "Buddha"; "Vad vi tror att vi blir" 2; "Mark Twain"; "Ångrar aldrig något som fick dig att le" 3; "Oscar Wilde"; "Var dig själv Alla andra är redan tagna"
Här skapas quotes.csv- filen i arbetskatalogen med ovanstående poster.
Som du ser har vi gått vidare csv.QUOTE_NONNUMERICtill quotingparametern. Det är en konstant som definieras av csvmodulen.
csv.QUOTE_NONNUMERICanger writerobjektet som citat ska läggas till runt de icke-numeriska posterna.
Det finns 3 andra fördefinierade konstanter som du kan skicka till quotingparametern:
csv.QUOTE_ALL- Angerwriterobjektet för att skriva CSV-fil med citat runt alla poster.csv.QUOTE_MINIMAL- Anger attwriterobjektet endast ska citera de fält som innehåller specialtecken ( avgränsare , citattecken eller några tecken i linjeterminator )csv.QUOTE_NONE- Angerwriterobjektet som ingen av posterna ska citeras. Det är standardvärdet.
CSV-filer med anpassat citattecken
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.
Rekommenderad läsning: Läs CSV-filer i Python
