Python - 为什么第二个 for 循环从第二行开始

Question

So I have these two for loops, the first one loops through a csv reader and the second loops through a csv DictReader. When results are printed I see that the first one is starting from the first row and the second is starting from the second row which I don't know why as it's a new loop. When I comment out the first one, the second one starts normally from the first row. Here is the code:

csvFile = open('contactscsv.csv', 'r')
headerReaderReader = csv.reader(csvFile)
headerReaderDict = csv.DictReader(csvFile)

for row in headerReaderReader:
    print(row)
    break

for row in headerReaderDict:
    print(row)
    break

Answer 1

You are reading from the same open file object, so your first headerReaderReader = csv.reader(csvFile) is starting from the first unread row and headerReaderDict = csv.DictReader(csvFile) is starting from the next unread row. If you reordered them to be

headerReaderDict = csv.DictReader(csvFile)
headerReaderReader = csv.reader(csvFile)

for row in headerReaderReader:
    print(row)
    break

for row in headerReaderDict:
    print(row)
    break

then headerReaderReader will start from the second row and headerReaderDict will start from the first.

If you really need to open 2 copies of the same file, you will need to maintain 2 different objects to avoid sharing the same pointer:

with open('contactscsv.csv', 'r') as csv1, open('contactscsv.csv', 'r') as csv2:
    headerReaderReader = csv.reader(csv1)
    headerReaderDict = csv.DictReader(csv2)