为什么Python CSV模块在运行程序后尝试打开时将CSV文件设为只读？

Question

I'm using a program (follows) to see the similarities in certain columns between two CSV files, then create a third when data matches certain specifications (two columns are the same but the third is not) so that I can update an e-mail list.

When I try to open the results.csv file after running the program however, Windows Excel will only open the program in read-only mode.

Any thoughts?

Here's my code:

import csv

sample_data = open("sample.csv", "r")
lib_data = open("library.csv", "r")
csv1 = csv.reader(sample_data)
csv2 = csv.reader(lib_data)

results = open("results.csv", "w")
res_csv = csv.writer(results)

limit = 1071
limit2 = 1001

x = 0
y = 0

while (y != limit):
    row1 = csv1.__next__()
    while (x != limit2):
        row2 = csv2.__next__()
        if (row1[0] == row2[3] and row1[1] == row2[2] and row1[2] != row2[5]):
            print ("SAMPLE:")
            print (row1[0], ", ", row1[1], ", ", row1[2])
            print ("LIBRARY:")
            print (row2[3], ", ", row2[2], ", ", row2[5])
            print("\n")
            res_csv.writerow(row1)
        x = x+1
    y = y+1
    x = 0
    lib_data.seek(0)

Answer 1

Use with to ensure files will be closed properly:

with open("sample.csv", "r") as sample_data:
    with open("library.csv", "r") as lib_data:
        with open("results.csv", "w") as results:
            # other code

You can even put several variables into one with if you're using Python >= 2.7.

Answer 2

Close the file

results.close()

Answer 3

Having the same problem when using python 2.7 and none of the solution solved my problem. Solution: just add "quoting", for example:

res_csv=csv.writer(results,quoting=csv.QUOTE_ALL). 

This solves my problem

Answer 4

You should try opening the file with specific permissions by importing os module and using file permission flags. Here is a link to a similar post - Write file with specific permissions in Python

Answer 5

You are leaving the files open. To close them, note that you have to first delete the csv object that uses the open file handle! Because of this, I rarely open the file handle separately from the csv reader/writer object.

So a better way to do this would be:

import csv

csv1 = csv.reader(open("sample.csv", "rb"))
csv2 = csv.reader(open("library.csv", "rb"))

res_csv = csv.writer(open("results.csv", "w"))

limit = 1071
limit2 = 1001

x = 0
y = 0

while (y != limit):
    row1 = csv1.__next__()
    while (x != limit2):
        row2 = csv2.__next__()
        if (row1[0] == row2[3] and row1[1] == row2[2] and row1[2] != row2[5]):
            print ("SAMPLE:")
            print (row1[0], ", ", row1[1], ", ", row1[2])
            print ("LIBRARY:")
            print (row2[3], ", ", row2[2], ", ", row2[5])
            print("\n")
            res_csv.writerow(row1)
        x = x+1
    y = y+1
    x = 0
    lib_data.seek(0)

del csv1
del csv2
del res_csv

This makes it more explicit that you have to delete the csv to close the file handle. Also note that the official csv docs state to open files in binary mode, to avoid line ending issues.

EDIT

As noted in the comments, I'm wrong about with closing the file even if the csv handle is still available. A quick test verified this, so proper usage is:

import csv

with open("sample.csv", "rb") as sample:
    csv1 = csv.reader(sample)
    with open("library.csv", "rb") as lib_data: # the csv handle for this file is never used
        with open("results.csv", "wb") as results:
            res_csv = csv.writer(results)

            limit = 1071
            limit2 = 1001

            x = 0
            y = 0

            while (y != limit):
                row1 = csv1.__next__()
                while (x != limit2):
                    row2 = csv2.__next__()
                    if (row1[0] == row2[3] and row1[1] == row2[2] and row1[2] != row2[5]):
                        print ("SAMPLE:")
                        print (row1[0], ", ", row1[1], ", ", row1[2])
                        print ("LIBRARY:")
                        print (row2[3], ", ", row2[2], ", ", row2[5])
                        print("\n")
                        res_csv.writerow(row1)
                    x = x+1
                y = y+1
                x = 0
                lib_data.seek(0)