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This is the implementation of codecs.Streamwriter.writelines for all 
Python versions that I've checked:
 def writelines(self, list):
 """ Writes the concatenated list of strings to the stream
 using .write().
 """
 self.write(''.join(list))
This may be a problem if the 'list' parameter is a generator. The 
generator may be returning millions of values, which the join will 
concatenate in memory. It can surprise the programmer with large 
memory use. I think join should only be used when you know the size of 
your input, and this method does not know this. I think the safe 
implementation of this method would be:
 def writelines(self, list):
 """ Writes the concatenated list of strings to the stream
 using .write().
 """
 write = self.write
 for value in list:
 write(value)
If a caller knows that it's input list would use a reasonable amount 
of memory, it can get the same functionality as before by doing 
stream.write(''.join(list)).