Use Python and do not use regular expressions libraries

Given a text file $$input$.$txt$,$ write a program to identify all the lexemes from the file $$input$.$txt$$ and write the lexemes separated by a single space into the file $$output$.$txt$.$ Please keep in mind that all comment lines $($lines that begin with $//),$ blank lines and extra white spaces are not included in the file $$output$.$txt$.$ Do not forget to place one space before and space after each lexeme. Note that the cin$>>$ is one lexeme.