Zapisywanie CSV za pomocą csv.DictWriter

Wprowadzenie

Podstawy csv.writer

import csv, io
buf = io.StringIO()
writer = csv.writer(buf)
writer.writerow(['name', 'age'])
writer.writerow(['Alice', 30])
print(buf.getvalue())

Zachowanie podczas cytowania

import csv, io
buf = io.StringIO()
writer = csv.writer(buf, quoting=csv.QUOTE_ALL)
writer.writerow(['Alice', 'NYC, NY', 30])
print(buf.getvalue())

csv.DictWriter

import csv, io
buf = io.StringIO()
fields = ['name', 'age']
writer = csv.DictWriter(buf, fieldnames=fields)
writer.writeheader()
writer.writerow({'name': 'Alice', 'age': 30})
print(buf.getvalue())

writerows() dla wielu wierszy

import csv, io
buf = io.StringIO()
writer = csv.DictWriter(buf, fieldnames=['x','y'])
writer.writeheader()
writer.writerows([{'x':1,'y':2},{'x':3,'y':4}])
print(buf.getvalue())

Niestandardowy separator

import csv, io
buf = io.StringIO()
writer = csv.writer(buf, delimiter='\t')
writer.writerow(['a', 'b', 'c'])
print(repr(buf.getvalue()))

Parametr extrasaction

import csv, io
buf = io.StringIO()
w = csv.DictWriter(buf, fieldnames=['name'], extrasaction='ignore')
w.writeheader()
w.writerow({'name': 'Alice', 'extra': 'ignored'})
print(buf.getvalue())

Zapis do rzeczywistego pliku

import csv, tempfile, os
tmp = tempfile.mktemp(suffix='.csv')
with open(tmp, 'w', newline='') as f:
    csv.writer(f).writerows([[1,2],[3,4]])
print(open(tmp).read())
os.unlink(tmp)

Dopisywanie do pliku CSV

import csv, io
buf = io.StringIO()
w = csv.writer(buf)
w.writerow(['x', 'y'])
print(buf.getvalue())

Strumieniowy zapis dużych ilości danych

import csv, io
buf = io.StringIO()
writer = csv.writer(buf)
for i in range(5):
    writer.writerow([i, i**2])
print(buf.getvalue())

Test pełnego obiegu

import csv, io
original = [{'name':'Alice','age':'30'},{'name':'Bob','age':'25'}]
buf = io.StringIO()
w = csv.DictWriter(buf, fieldnames=['name','age'])
w.writeheader()
w.writerows(original)
buf.seek(0)
read_back = list(csv.DictReader(buf))
print(read_back == original)

Szybkie sprawdzenie

Podsumowanie

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