Selles õpetuses õpime näidete abil kirjutama Pythonis erineva vorminguga CSV-faile.
csvSelle ülesande jaoks kasutame eranditult Pythoni sisseehitatud moodulit. Kuid kõigepealt peame mooduli importima järgmiselt:
import csv
Oleme juba käsitlenud põhitõdesid, kuidas csvmoodulit kasutada CSV-failide lugemiseks ja kirjutamiseks. Kui teil pole csvmooduli kasutamise kohta ideed , vaadake meie õpetust Python CSV-st: CSV-failide lugemine ja kirjutamine
Csv.writeri () põhikasutus
Vaatame csv.writer()põhinäidet olemasolevate teadmiste värskendamiseks.
Näide 1: kirjutage CSV-failidesse csv.writer () -ga
Oletame, et tahame kirjutada CSV-faili järgmiste kirjetega:
SN, nimi, kaastöö 1, Linus Torvalds, Linuxi tuum 2, Tim Berners-Lee, veeb 3, Guido van Rossum, Pythoni programmeerimine
Siin on, kuidas me seda teeme.
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"))
Kui käivitame ülaltoodud programmi, luuakse praeguses töökataloogis antud kirjetega fail innovators.csv .
Siin avasime faili innovators.csv kirjutamisrežiimis open()funktsiooni abil.
Failide Pythonis avamise kohta lisateabe saamiseks külastage lehte Python File Input / Output
Järgmisena kasutatakse csv.writer()funktsiooni writerobjekti loomiseks . writer.writerow()Funktsiooni kasutatakse seejärel kirjutada ühe rea CSV faili.
Näide 2: Mitme rea kirjutamine kirjutusribadega ()
Kui peame kahemõõtmelise loendi sisu CSV-faili kirjutama, saame seda teha järgmiselt.
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)
Programmi väljund on sama, mis näites 1 .
Siin edastatakse meie kahemõõtmeline loend writer.writerows()funktsioonile, mis kirjutab loendi sisu CSV-faili.
Vaatame nüüd, kuidas saame CSV-faile kirjutada erinevates vormingutes. Seejärel õpime csv.writer()funktsiooni nende kirjutamiseks kohandama .
CSV-failid kohandatud eraldajatega
Vaikimisi kasutatakse CSV-failis eraldajat koma. Mõnes CSV-failis saab aga kasutada komakohti lisaks eraldusmärkidele. Vähesed populaarsed on |ja .
Oletame, et soovime kasutada näite 1 failis innovators.csv| eraldajana . Selle faili kirjutamiseks võime funktsioonile edastada täiendava parameetri .delimitercsv.writer()
Võtame näite.
Näide 3: CSV-faili kirjutamine, kasutades torude eraldajat
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)
Väljund
SN | Nimi | Kaastöö 1 | Linus Torvalds | Linuxi kernel 2 | Tim Berners-Lee | Veeb 3 | Guido van Rossum | Pythoni programmeerimine
Nagu näeme, delimiter = '|'aitab valikuline parameeter määrata writerobjekti, mis CSV-failil peaks olema |eraldaja.
Tsitaatidega CSV-failid
Mõnel CSV-failil on jutumärgid iga kirje või mõne ümber.
Võtame näiteks quotes.csv järgmiste kirjetega:
"SN"; "Nimi"; "Tsitaadid" 1; "Buddha"; "Mida me arvame, et me saame" 2; "Mark Twain"; "Ärge kunagi kahetse midagi, mis pani teid naeratama" 3; "Oscar Wilde"; "Ole ise kõik teised on juba võetud "
Kasutades csv.writer()vaikimisi ei lisa neid tsitaate sissekanded.
Nende lisamiseks peame kasutama veel ühte valikulist parameetrit nimega quoting.
Võtame näite selle kohta, kuidas tsiteerimist saab kasutada mittearvuliste väärtuste ümber ja ;eraldajatena.
Näide 4: kirjutage jutumärkidega CSV-failid
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)
Väljund
"SN"; "Nimi"; "Tsitaadid" 1; "Buddha"; "Mida me arvame, et me saame" 2; "Mark Twain"; "Ärge kunagi kahetse midagi, mis pani teid naeratama" 3; "Oscar Wilde"; "Ole ise kõik teised on juba võetud "
Siin luuakse fail quotes.csv töökataloogis ülaltoodud kirjetega.
Nagu näete, oleme läbinud csv.QUOTE_NONNUMERICselle quotingparameetri. See on csvmooduli määratletud konstant .
csv.QUOTE_NONNUMERICmäärab writerobjekti, mille jutumärgid tuleks lisada mitte-numbriliste kirjete ümber.
quotingParameetrile saate edastada veel 3 eelmääratud konstanti :
csv.QUOTE_ALL- Määrabwriterobjekti, kuhu CSV-fail kirjutada jutumärkidega kõigi kirjete ümber.csv.QUOTE_MINIMAL- määrabwriterobjekti tsiteerida ainult neid välju, mis sisaldavad erimärke ( eraldaja , jutumärk või mis tahes tähemärgid lineterminaatoris )csv.QUOTE_NONE- Määrabwriterobjekti, mida ühtegi kirjet ei tohiks tsiteerida. See on vaikeväärtus.
Kohandatud jutumärgiga CSV-failid
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.
Soovitatav lugemine: lugege Pythonis CSV-faile
