Python中的语句被忽略

Question

I have two functions. The first creates a new CSV file (from an existing CSV). The second appends the same data to the new CSV, but in a slightly different order of the rows.

When I run this together all in one file the first function works but the second does not. However when I tried putting the second function in a separate file then calling it in the first script, it did work, albeit I had to enter the input twice.

What do I need to change to get the second function to run properly?

import csv
export = raw_input('>')
new_file = raw_input('>')

ynabfile = open(export, 'rb')
reader = csv.reader(ynabfile)

def create_file():
    with open(new_file, 'wb') as result:
        writer = csv.writer(result)
        for r in reader:
            writer.writerow((r[3], r[5], r[6],r[7], r[7],
                r[8],r[8],r[9],r[10]))

def append():
    with open(new_file, 'ab') as result2:
        writer2 = csv.writer(result2)
        for i in reader:
            writer.writerow((r[3], r[5], r[6], r[7], r[7],
                r[8], r[8], r[10], r[9]))

create_file()

append()

I'm new to Python and programming in general, so if there is an all around better way to do this, I'm all ears.

Answer 1

The csv reader has already read the entire file pointed to by ynabfile , so on the second call (or any subsequent calls) to either create_file or append will not be able to fetch any more data using the reader until the file pointer is sent back to the beginning. In your case, a quick fix would be this:

create_file()
ynabfile.seek(0)
append()

I recommend restructuring your code a bit to avoid pitfalls like this. A few recommendations:

• Read all the contents in ynabfile into another list instead, if you can fit the entirety of the file into memory
• Have create_file and append take parameter of input and output file names
• Alternatively, have those two functions take the file pointer ( ynabfile in this case), and ensure that it is seeked to the beginning then create a new csv.reader instance using that.