Šajā apmācībā mēs ar piemēriem iemācīsimies rakstīt CSV failus dažādos formātos Python.
csvŠim uzdevumam mēs izmantosim tikai Python iebūvēto moduli. Bet vispirms mums būs jāimportē modulis kā:
import csv
Mēs jau esam apskatījuši pamatus, kā izmantot csvmoduli, lai lasītu un ierakstītu CSV failos. Ja jums nav ideju par csvmoduļa izmantošanu, skatiet mūsu apmācību par Python CSV: lasiet un rakstiet CSV failus
Csv.writer () pamata lietojums
Apskatīsim pamata piemēru, kā izmantot csv.writer()esošās zināšanas.
1. piemērs: ierakstiet CSV failos, izmantojot csv.writer ()
Pieņemsim, ka mēs vēlamies uzrakstīt CSV failu ar šādiem ierakstiem:
SN, nosaukums, 1. ieguldījums, Linuss Torvalds, Linux kodols 2, Tims Berners-Lī, 3. tīmeklis, Gvido van Rosums, Python programmēšana
Lūk, kā mēs to darām.
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"))
Kad mēs palaist minēto programmu, kas ir innovators.csv fails tiek izveidots pašreizējā darba direktoriju ar dotajiem ierakstiem.
Šeit mēs esam atvēruši failu innovators.csv rakstīšanas režīmā, izmantojot open()funkciju.
Lai uzzinātu vairāk par failu atvēršanu Python, apmeklējiet vietni: Python File Input / Output
Tālāk csv.writer()funkcija tiek izmantota writerobjekta izveidošanai. Pēc writer.writerow()tam šo funkciju izmanto, lai CSV failā ierakstītu atsevišķas rindas.
2. piemērs: Vairāku rindu rakstīšana ar rakstītājrindām ()
Ja mums ir jāieraksta divdimensiju saraksta saturs CSV failā, mēs to varam izdarīt šādi.
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)
Programmas izvade ir tāda pati kā 1. piemērā .
Šeit mūsu divdimensiju saraksts tiek nodots writer.writerows()funkcijai saraksta satura ierakstīšanai CSV failā.
Tagad redzēsim, kā mēs varam rakstīt CSV failus dažādos formātos. Pēc tam mēs uzzināsim, kā pielāgot csv.writer()funkciju to rakstīšanai.
CSV faili ar pielāgotiem atdalītājiem
Pēc noklusējuma CSV failā kā atdalītājs tiek izmantots komats. Tomēr dažos CSV failos var izmantot atdalītājus, kas nav komats. Daži populāri ir |un .
Pieņemsim, ka mēs vēlamies, lai izmantotu |kā atdalītāju ar innovators.csv failā 1. piemērs . Lai rakstītu šo failu, mēs varam nodot funkcijai papildu delimiterparametru csv.writer().
Ņemsim piemēru.
3. piemērs: CSV faila rakstīšana ar cauruļu atdalītāju
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)
Rezultāts
SN | Vārds | Ieguldījums 1 | Linus Torvalds | Linux kodols 2 | Tims Berners-Lī | Globālais tīmeklis 3 | Gvido van Rossums | Python programmēšana
Kā mēs redzam, izvēles parametrs delimiter = '|'palīdz norādīt writerobjektu, kas CSV failam vajadzētu būt |kā atdalītājam.
CSV faili ar Citātiem
Dažos CSV failos ir pēdiņas ap katru vai dažus ierakstus.
Ņemsim par piemēru quotes.csv ar šādiem ierakstiem:
"SN"; "Vārds"; "Citāti" 1; "Buda"; "Tas, par ko mēs domājam, ka mēs kļūstam" 2; "Marks Tvens"; "Nekad nenožēlojiet neko tādu, kas lika jums pasmaidīt" 3; "Oskars Vailds"; "Esi pats visi pārējie jau ir paņemti "
Izmantojot csv.writer()noklusējumu, šie pēdiņas ierakstiem netiks pievienoti.
Lai tos pievienotu, mums būs jāizmanto vēl viens izvēles parametrs ar nosaukumu quoting.
Ņemsim piemēru, kā citēšanu var izmantot ap skaitliskām vērtībām un ;kā atdalītājus.
4. piemērs: rakstiet CSV failus ar pēdiņām
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)
Rezultāts
"SN"; "Vārds"; "Citāti" 1; "Buda"; "Tas, par ko mēs domājam, ka mēs kļūstam" 2; "Marks Tvens"; "Nekad nenožēlojiet neko tādu, kas lika jums pasmaidīt" 3; "Oskars Vailds"; "Esi pats visi pārējie jau ir paņemti "
Šeit darba katalogā ar iepriekš minētajiem ierakstiem tiek izveidots fails quotes.csv .
Kā redzat, mēs esam pārgājuši csv.QUOTE_NONNUMERICuz quotingparametru. Tā ir konstante, ko nosaka csvmodulis.
csv.QUOTE_NONNUMERICnorāda writerobjektu, kas pēdiņās jāpievieno ap skaitliskajiem ierakstiem.
quotingParametram var nodot vēl 3 iepriekš definētas konstantes :
csv.QUOTE_ALL- Norādawriterobjektu CSV faila rakstīšanai ar pēdiņām ap visiem ierakstiem.csv.QUOTE_MINIMAL- norādawriterobjektu, lai citētu tikai tos laukus, kuros ir īpašas rakstzīmes ( norobežotājs , pēdiņa vai jebkuras rakstzīmes lineterminatorā )csv.QUOTE_NONE- Norādawriterobjektu, kuru neviens no ierakstiem nedrīkst citēt. Tā ir noklusējuma vērtība.
CSV faili ar pielāgotu pēdiņu rakstzīmi
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.
Ieteicamā literatūra: lasiet CSV failus Python
