Although declared *exactly equivalent* to printf in the doc, PyUnicode_FromFormat could generate different result from printf with the same format.

For example:

from ctypes import pythonapi, py_object, c_int
f = getattr(pythonapi, 'PyUnicode_FromFormat')
f.restype = py_object
f(b'%010.5d', c_int(100))
'0000000100'

while printf outputs:

printf("%010.5d\n", 100);
     00100

I use both gcc and clang to compile and get the same result. gcc gives me a warning:

warning: '0' flag ignored with precision and ‘%d’ gnu_printf format

I am not sure this should be fixed. It seems the change could break backwards compatibility.