python - Is there a way to only replace part of format string? -

example:

format_string  = "http://somedomain.com/%s/%d" format_string %= ('somestring', %d) print(format_string) >>> http://somedomain.com/somestring/%d 

is there way this?

the string interpolation requires have 1 item each "conversion specification" in string. however, can escape "conversion specification" % ...

format_string = 'http://somedomain.com/%s/%%d' print(format_string % 'foo') 

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of course, complete "hack" (that work if you're trying replace %s) put conversion string in place of original one...:

format_string = '%s%s' print(format_string % ('foo', '%s')) 

again, doesn't work in scenario...

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other options use .format style string formatting and write own formatter. note, isn't faint @ heart -- here's basic example¹:

import string  class myformat(string.formatter):     def vformat(self, format_string, args, kwargs):         out_lst = []         iargs = iter(args)         tup in self.parse(format_string):             literal_text, _, format_spec, _ = tup             if literal_text:                 out_lst.append(literal_text)             if format_spec:                 try:                     out_lst.append(format_spec % next(iargs))                 except stopiteration:                     out_lst.append('{:' + format_spec + '}')         return ''.join(out_lst)   print(myformat().format('foo {:%s} {:%d}', 'a', 10))  # foo 10 print(myformat().format('foo {:%s} {:%d}', 'a'))  # foo {:%d} 

^{1this first attempt ever write 1 of these ... it's possible can done more cleanly , i'll happily accept improvements...}