CODEWITHSUNDEEP
python
Ian Langmore
Ian Langmore

Reputation: 2939

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

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.

Upvotes: 47

Views: 11294

Answers (6)

Carl Smith
Carl Smith

Reputation: 728

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()

Upvotes: 28

Andrei Cioara
Andrei Cioara

Reputation: 3664

For completeness, I made a snippet with the following code, based on the accepted answer.

import sys; sys.stdin = open('/dev/tty'); import pdb; pdb.set_trace();

Upvotes: 3

C. Reed
C. Reed

Reputation: 2452

Using the ripdb module (pip install ripdb) solved this issue for me.

Upvotes: 5

thyme
thyme

Reputation: 480

I ran into this exact problem today. I found that Winpdb works perfectly.

Upvotes: 1

Nate Ferrero
Nate Ferrero

Reputation: 1458

You may want to look at how the Celery RDB (Remote Debugger) contrib module works:

https://github.com/celery/celery/blob/master/celery/contrib/rdb.py

It seems to involve a lot of stream processing, but I have tested it, and it works by allowing you to telnet into a new local network port. It's not the much better ipdb, but simply pdb.

Upvotes: 2

tito
tito

Reputation: 13251

The thing is: cat will not stop sending data because your script is currently debugging. And when you going to trace, then stdin is still filled by cat + your keyboard. You need to choose one of them.

You can read the whole stdin, and then, set_trace() will be not filled by stdin:

sys.stdin.read()
pdb.set_trace()

Upvotes: 5

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