file is overwriten in python,when open in append mode

Question

WriteFile1() Code snip:

try:
    iOutputFile = open(IFilePath, "a")
    if iOutputFile == 0:
        return

    csvInfoWriter = csv.writer(iOutputFile,  delimiter=',', lineterminator='\n')

    lenBuff = len(g_Hash)
    for value in g_Hash.itervalues():
        iValueLen = len(value)
        for index in range(0, iValueLen):
            csvInfoWriter.writerow(value[index])


    iOutputFile.close()

 except:
    print sys.exc_type

I'm reading one files contents, storing those in dict g_Hash.

After reading 1000 records,I'm calling WriteFile1() to write file, and I do clear contents from dict g_Hash [By calling ClearRec() ]. Everytime I do call WriteFile1() it overwrites my outputfile.

Please help me, I want to append the data, not wanted to overwrite..

Edit: After removing this from code, still the problem occurs.

 if iOutputFile == 0:
        return

Update:

ClearRec() Code:

        WriteFile1()
        g_Hash.clear()

----------- Does ClearRec() will cause any problem? --------

its python, not java. All functionality works file, just overwrite problem. — Emma, Jul 04 '13 at 13:59
You may have to post all of your code (if it's long then add a pastebin link). I wrapped the snippet in a function (without the try/except) and called WriteFile1() twice with a different dictionary and no overwriting occurred. I used Python 2.7.3 running on Windows 7. — Talvalin, Jul 04 '13 at 15:47

score 3 · Accepted Answer · answered Jul 04 '13 at 14:35

You need to change the append to "a+"

For a little more reference http://docs.python.org/2/library/functions.html#open

Modes 'r+', 'w+' and 'a+' open the file for updating (note that 'w+' truncates the file). Append 'b' to the mode to open the file in binary mode, on systems that differentiate between binary and text files; on systems that don’t have this distinction, adding the 'b' has no effect.

score 2 · Answer 2 · answered Jul 04 '13 at 14:00

2

Remove following line. It always be evaluated as False.

if iOutputFile == 0:
    return

Builtin open in Python return file object, not file descriptor.

>>> f = open('1', 'a')
>>> f
<open file '1', mode 'a' at 0x000000000281C150>
>>> type(f)
<type 'file'>
>>> f == 0
False

answered Jul 04 '13 at 14:00

falsetru

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@Emma, Then, check if any `open(IFilePath, "w..")` occur in your code. – falsetru Jul 04 '13 at 14:05
nope only in this function I'm writing file, no where else is written – Emma Jul 04 '13 at 14:07
@Emma, If you run you code without `try ... except ...`, any error occur? If it print error, traceback, please post it as is. – falsetru Jul 04 '13 at 14:16
@Emma, **without** `try .. except ..`. – falsetru Jul 04 '13 at 14:20

file is overwriten in python,when open in append mode

2 Answers2