[英]How to address: Python import of file with .csv Dictreader fails on undefined character
[英]“Doing work” on csv DictReader fails
我正在编写一个脚本,我需要将CSV读入DictReader
,在字段上做一些工作(数据调整),然后通过DictWriter
将DictReader
输出到csv。
如果我读取CSV然后写下Dict,则该过程有效。
#Create the sample file
headers = ['Symbol', 'Price', 'Date', 'Time', 'Change', 'Volume']
rows = [{'Symbol':'AA', 'Price':39.48, 'Date':'6/11/2007',
'Time':'9:36am', 'Change':-0.18, 'Volume':181800},
{'Symbol':'AIG', 'Price': 71.38, 'Date':'6/11/2007',
'Time':'9:36am', 'Change':-0.15, 'Volume': 195500},
{'Symbol':'AXP', 'Price': 62.58, 'Date':'6/11/2007',
'Time':'9:36am', 'Change':-0.46, 'Volume': 935000},
]
#Open sample file
with open('stocks.csv','w') as f:
f_csv = csv.DictWriter(f, headers)
f_csv.writeheader()
f_csv.writerows(rows)
#Output the dict
with open('stocks.csv', 'r') as file:
csvread = csv.DictReader(file, delimiter=',')
with open('out.csv', 'w') as out:
headertowrite = ['Time', 'Symbol', 'NewColumn']
writer = csv.DictWriter(out, headertowrite, extrasaction='ignore')
writer.writeheader()
writer.writerows(csvread)
#Works!
但是 - 如果我添加一个新列,似乎我丢失了DictReader中的所有数据:
headers = ['Symbol', 'Price', 'Date', 'Time', 'Change', 'Volume']
rows = [{'Symbol':'AA', 'Price':39.48, 'Date':'6/11/2007',
'Time':'9:36am', 'Change':-0.18, 'Volume':181800},
{'Symbol':'AIG', 'Price': 71.38, 'Date':'6/11/2007',
'Time':'9:36am', 'Change':-0.15, 'Volume': 195500},
{'Symbol':'AXP', 'Price': 62.58, 'Date':'6/11/2007',
'Time':'9:36am', 'Change':-0.46, 'Volume': 935000},
]
with open('stocks.csv','w') as f:
f_csv = csv.DictWriter(f, headers)
f_csv.writeheader()
f_csv.writerows(rows)
with open('stocks.csv', 'r') as file:
csvread = csv.DictReader(file, delimiter=',')
for row in csvread:
row['NewColumn'] = '1'
with open('out.csv', 'w') as out:
headertowrite = ['Time', 'Symbol', 'NewColumn']
writer = csv.DictWriter(out, headertowrite, extrasaction='ignore')
writer.writeheader()
writer.writerows(csvread)
#Out.csv is blank!
有没有办法在我写之前可以在DictReader上执行工作?
由于你的第一个for
循环完全消耗了csvread,我们的with
语句将输出一个空白文件,你可能会注意到。
你应该:
- >将行保存到变量中
import csv
headers = ['Symbol', 'Price', 'Date', 'Time', 'Change', 'Volume']
rows = [{'Symbol':'AA', 'Price':39.48, 'Date':'6/11/2007',
'Time':'9:36am', 'Change':-0.18, 'Volume':181800},
{'Symbol':'AIG', 'Price': 71.38, 'Date':'6/11/2007',
'Time':'9:36am', 'Change':-0.15, 'Volume': 195500},
{'Symbol':'AXP', 'Price': 62.58, 'Date':'6/11/2007',
'Time':'9:36am', 'Change':-0.46, 'Volume': 935000}]
with open('stocks.csv','w') as f:
f_csv = csv.DictWriter(f, headers)
f_csv.writeheader()
f_csv.writerows(rows)
with open('stocks.csv', 'r') as file:
csvread = csv.DictReader(file, delimiter=',')
rows = []
for row in csvread:
row['NewColumn'] = '1'
rows.append(row)
with open('out.csv', 'w') as out:
headertowrite = ['Time', 'Symbol', 'NewColumn']
writer = csv.DictWriter(out, headertowrite, extrasaction='ignore')
writer.writeheader()
writer.writerows(rows)
要么
- >在将输出文件的with语句中进行修改(您读取一行,修改并编写它。
import csv
headers = ['Symbol', 'Price', 'Date', 'Time', 'Change', 'Volume']
rows = [{'Symbol':'AA', 'Price':39.48, 'Date':'6/11/2007',
'Time':'9:36am', 'Change':-0.18, 'Volume':181800},
{'Symbol':'AIG', 'Price': 71.38, 'Date':'6/11/2007',
'Time':'9:36am', 'Change':-0.15, 'Volume': 195500},
{'Symbol':'AXP', 'Price': 62.58, 'Date':'6/11/2007',
'Time':'9:36am', 'Change':-0.46, 'Volume': 935000}]
with open('stocks.csv','w') as f:
f_csv = csv.DictWriter(f, headers)
f_csv.writeheader()
f_csv.writerows(rows)
with open('stocks.csv', 'r') as file:
csvread = csv.DictReader(file, delimiter=',')
with open('out.csv', 'w') as out:
headertowrite = ['Time', 'Symbol', 'NewColumn']
writer = csv.DictWriter(out, headertowrite, extrasaction='ignore')
writer.writeheader()
for row in csvread:
row['NewColumn'] = '1'
writer.writerow(row)
照顾自己! 这是writerow
不writerows
在第二个解决方案!
请注意,我还强烈推荐第二种解决方案,它在内存消耗方面更具可扩展性。
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