How To Debug Python Cli That Takes Stdin?

I'm trying to debug a Python CLI I wrote that can take its arguments from stdin. A simple test case would have the output of echo 'test' | python mytool.py be equivalent to the ou

Solution 1:

Another option is to create you own Pdb object, and set there the stdin and stdout. My proof of concept involves 2 terminals, but for sure some work can be merged some kind of very unsecure network server.

1. Create two fifos:

   mkfifo fifo_stdin
   mkfifo fifo_stdout
   

2. In one terminal, open stdout on background, and write to stdin:

   cat fifo_stdout &
   cat > fifo_stdin
   

3. In your python code/console create the pdb object, and use it:

   import pdb
   mypdb=pdb.Pdb(stdin=open('fifo_stdin','r'), stdout=open('fifo_stdout','w'))
   ...
   mypdb.set_trace()
   ...
   

4. Profit!

You should be able to use pdb on the first console.

The only drawback is having to use your custom pdb, but some monkey patching at init (PYTHONSTARTUP or similar) can help:

import pdb
mypdb=pdb.Pdb(stdin=open('fifo_stdin','r'), stdout=open('fifo_stdout','w'))
pdb.set_trace=mypdb.set_trace

Solution 2:

You can use another file descriptor. With bash you can create a new file descriptor with:

exec 3<> test.txt

And then on your python file have something like:

#!/usr/bin/python

# Use fd 3 as another stdin file.
import osstdin=os.fdopen(3)

while True:
    s=stdin.readline()
    import pdb; pdb.set_trace()
    printlen(s)

Just runing your script will use that test.txt as input, and you can use stdin on stdin. It can be used as well with pipes if you need.

Solution 3:

Your controlling TTY is still a terminal, right? Use this instead of pdb.set_trace.

deftty_pdb():
    from contextlib import (_RedirectStream,
                            redirect_stdout, redirect_stderr)
    classredirect_stdin(_RedirectStream):
        _stream = 'stdin'withopen('/dev/tty', 'r') as new_stdin, \
         open('/dev/tty', 'w') as new_stdout, \
         open('/dev/tty', 'w') as new_stderr, \
         redirect_stdin(new_stdin), \
         redirect_stdout(new_stdout), redirect_stderr(new_stderr):
        __import__('pdb').set_trace()

Haven't gotten readline to autocomplete under these circumstances. Up arrow won't work either, or any other of the readline niceties.

Solution 4:

When you use pdb(or any other python debugger) it acquires stdin for debug commands, that's why you get NameError: name 'test' is not defined.

For example this command will quit debugger at the begging of a runtime and you wont get this error(nor interactive debugging) for one run:

(echo cont;echo "test") | python -m pdb mytool.py