Python: Why two global variables have different behaviours? [duplicate]

Question

I have a piece of code like this further down.

With this code I get a:

local variable 'commentsMade' referenced before assignment

Why do I need a 'global commentsMade' statement in the first function but I don't need with TARGET_LINES? (using Python2.7)

TARGET_LINE1 = r'someString'
TARGET_LINE2 = r'someString2'
TARGET_LINES = [TARGET_LINE1, TARGET_LINE2]
commentsMade = 2

def replaceLine(pattern, replacement, line, adding):

    #global commentsMade  # =========> Doesn't work. Uncommenting this does!!!!

    match = re.search(pattern, line)
    if match:
        line = re.sub(pattern, replacement, line)
        print 'Value before = %d ' % commentsMade
        commentsMade += adding
        print 'Value after = %d ' % commentsMade
    return line

def commentLine(pattern, line):
    lineToComment = r'(\s*)(' + pattern + r')(\s*)$'
    return replaceLine(lineToComment, r'\1<!--\2-->\3', line, +1)

def commentPomFile():
    with open('pom.xml', 'r+') as pomFile:
        lines = pomFile.readlines()
        pomFile.seek(0)
        pomFile.truncate()

        for line in lines:
            if commentsMade < 2:

                for targetLine in TARGET_LINES: # ===> Why this works???

                    line = commentLine(targetLine, line)

            pomFile.write(line)

if __name__ == "__main__":
    commentPomFile()

Tom Karzes · Accepted Answer · 2016-06-18 02:53:25Z

1

If you make an assignment to a variable in the body of a function, then Python treats the variable as local (unless you declare it global). If you just read the value within the body of a function, without assigning to it, then it looks for the variable in a higher scope (e.g., parent function or global).

So in your case, the difference is that you assign to commentsMade, which makes it local, but you don't assign to TARGET_LINES, so it looks for a global definition for it.

answered Jun 18, 2016 at 2:53

Tom Karzes

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