ZipFile allows to add the same file to archive twice. I bet it is not
intended behavior for many users who would like to either replace file
inside of archive or get runtime warning about duplicate file to be
added. http://code.google.com/p/gvn/issues/detail?id=63


from zipfile import ZipFile

zt=ZipFile("ziptest.zip","w")
zt.write("ziptest.py")
zt.write("ziptest.py")
zt.close()

I think a warning would be sensible here. The behavior is certainly not
what I would expect.

How about adding optional "replace=True" attribute to the write method?
So that people who are not aware enough to adjust the code and handle
new warning could still get valid archives.

The mechanism for throwing an error has been written, however for the
case of a duplicated filename, it appears to have been deliberatly not
been used by the original author.:

 def _writecheck(self, zinfo):
        """Check for errors before writing a file to the archive."""
        if zinfo.filename in self.NameToInfo:
            if self.debug:      # Warning for duplicate names
                print "Duplicate name:", zinfo.filename
        if self.mode not in ("w", "a"):
            raise RuntimeError, 'write() requires mode "w" or "a"'
        ...

Putting a 'replace=True' switch seems a little clumsy, it would be much
better to raise an error, or allow the user a way to globally control
what happens in this case, i.e. overwrite the existing file or drop it.
 Adding a global behaviour switch seems to be the best way to preserve
backwards compatibility.

What do people think is the best way?

-- Martin