Use pdb.set_trace() in a script that reads stdin via a pipe

Question

I have a python script that reads stdin via a pipe, and I cannot seem to use it with pdb.set_trace().

my_script.py:

#!/usr/bin/env python import sys import pdb  def main():     for line in sys.stdin:         print "Printing a line: " +line  if __name__=='__main__':     status = main() 

Suppose tempfile.csv is some file with two lines,

$ cat tempfile.csv  line1 line2 

then I can run my script with: $ cat tempfile.csv | ./my_script.py, and everything is fine:

$ cat tempfile.csv | ./my_script.py  Printing a line:  line1  Printing a line:  line2 

On the other hand, if I put pdb.set_trace() anywhere then I get an error. For example, putting pdb.set_trace() below def main(), then I get

$ cat tempfile.csv | ./my_script.py  > /home/ilangmore/mobiuss/TM/branches/hadooprotype/my_script.py(7)main() -> for line in sys.stdin: (Pdb) *** NameError: name 'line1' is not defined (Pdb) *** NameError: name 'line2' is not defined (Pdb)  Traceback (most recent call last):   File "./my_script.py", line 11, in <module>     status = main()   File "./my_script.py", line 7, in main     for line in sys.stdin:   File "./my_script.py", line 7, in main     for line in sys.stdin:   File "/usr/lib/python2.7/bdb.py", line 48, in trace_dispatch     return self.dispatch_line(frame)   File "/usr/lib/python2.7/bdb.py", line 67, in dispatch_line     if self.quitting: raise BdbQuit bdb.BdbQuit 

Note that my question is probably related to this question (i.e. pdb by default reads from stdin), but I need more help.

Answer 1

Here's an example of what worked for me:

import sys import pdb  lines = sys.stdin.readlines() sys.stdin = open("/dev/tty") pdb.set_trace() 

Edit: since 3.7 you no longer need to import pdb for set_trace, it is available as breakpoint, so the above only requires a sys import.

import sys  lines = sys.stdin.readlines() sys.stdin = open("/dev/tty") breakpoint() 

You may wish to replace sys.stdin.readlines() above with the iterable fileinput.input() (which defaults to sys.stdin if the list of files in sys.argv[1:] is empty) like so:

import fileinput import sys  lines = fileinput.input() sys.stdin = open("/dev/tty") breakpoint()