file - Why is Python giving me "an integer is required" when it shouldn't be?

Question

I have a save function within my Python program which looks like this:

def Save(n):
    print("S3")
    global BF
    global WF
    global PBList
    global PWList
    print(n)
    File = open("C:KingsCaptureSaves" + n + "BF.txt", "w")
    pickle.dump(BF, File)
    File = open("C:KingsCaptureSaves" + n + "WF.txt", "w")
    pickle.dump(WF, File)
    File = open("C:KingsCaptureSaves" + n + "PBList.txt", "w")
    pickle.dump(PBList, File)
    File = open("C:KingsCaptureSaves" + n + "PWList.txt", "w")
    pickle.dump(PWList, File)

Here, n is "1".

I get an error looking like this:

  File "C:/Python27/KingsCapture.py", line 519, in Save
    File = open("C:KingsCaptureSaves" + n + "BF.txt", "w")
TypeError: an integer is required

Upon doing the same loading within the shell, I get no errors:

>>> File = open("C:KingsCaptureTestList.txt", "r")
>>> File = open("C:KingsCaptureTestList.txt", "w")
>>> n = "1"
>>> File = open("C:KingsCaptureSaves" + n + "BF.txt", "r")
>>> File = open("C:KingsCaptureSaves" + n + "BF.txt", "w")

Why is this having a problem?

Answer 1

You probably did a star import from the os module:

>>> open("test.dat","w")
<open file 'test.dat', mode 'w' at 0x1004b20c0>
>>> from os import *
>>> open("test.dat","w")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: an integer is required

so you're using the wrong open function. (I suppose you could've simply done from os import open, but that's less likely.) In general this import style should be avoided, as should use of global, where practical.