Python：读取 CSV 文件时缺少第一行

Question

I am trying to test the data in a CSV file. First I used the CSV library to put the contents of a CSV file into a dictionary:

#CSV is the CSV file
csvfile = open(CSV)
CSVCont = csv.DictReader(csvfile)

I did a few tests without messing with the dictionary and I wanted to print out the contents. I used this code:

for row in CSVCont:
    print(row)

The output I got was missing the first line of data. My guess is the file was read wrong. Can someone please help me with this?

Answer 1

By default, csv.DictReader consumes the first line and uses it as the header row, used as the keys in the dictionaries that represent the rows.

If your first row should not be treated as the header row, you should provide the fieldnames argument as a list of headers.

If you'd rather not use headers at all, just use csv.reader instead (which will emit each row as a tuple instead of a dictionary).

For example, with this file:

a,b,c
d,e,f
g,h,i

Note the difference:

with open('test.csv') as f:
    reader = csv.DictReader(f)
    for row in reader:
        print(row)

outputs

OrderedDict([('a', 'd'), ('b', 'e'), ('c', 'f')])
OrderedDict([('a', 'g'), ('b', 'h'), ('c', 'i')])

While

with open('test.csv') as f:
    reader = csv.DictReader(f, fieldnames=['1', '2', '3'])
    for row in reader:
        print(row)

outputs

OrderedDict([('1', 'a'), ('2', 'b'), ('3', 'c')])
OrderedDict([('1', 'd'), ('2', 'e'), ('3', 'f')])
OrderedDict([('1', 'g'), ('2', 'h'), ('3', 'i')])