Apply the second version of SF patch http://www.python.org/sf/536241
Add a method zfill to str, unicode and UserString and change
Lib/string.py accordingly.
This activates the zfill version in unicodeobject.c that was
commented out and implements the same in stringobject.c. It also
adds the test for unicode support in Lib/string.py back in and
uses repr() instead() of str() (as it was before Lib/string.py 1.62)
diff --git a/Doc/lib/libstdtypes.tex b/Doc/lib/libstdtypes.tex
index 6f819e9..e7275ce 100644
--- a/Doc/lib/libstdtypes.tex
+++ b/Doc/lib/libstdtypes.tex
@@ -694,6 +694,12 @@
Return a copy of the string converted to uppercase.
\end{methoddesc}
+\begin{methoddesc}[string]{zfill}{width}
+Return the numeric string left filled with zeros in a string
+of length \var{width}. The original string is returned if
+\var{width} is less than \code{len(\var{s})}.
+\end{methoddesc}
+
\subsubsection{String Formatting Operations \label{typesseq-strings}}