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Tips and Tricks for the Python Interpreter

Tagged with: Python

I have seen a lot of people switch over to using ipython, bpython, etc to get auto-complete support without realizing that the standard interpreter does have this functionality.

To enable auto-complete support in the python interpreter you need to create a python startup file that enables readline support. A python startup file is just a bunch of python code that gets executed at startup of the interpreter. To do this you just setup PYTHONSTARTUP in your ~/.bashrc and then create a ~/ file:

    import readline
except ImportError:
    print("Module readline not available.")
    import rlcompleter
    readline.parse_and_bind("tab: complete")

Now when you are in python you have tab completion on importing, calling methods on a module, etc.

>>> import o
object(  oct(     open(    or       ord(     os

I always end up using the pretty print module for viewing long lists and strings in the interpreter so I prefer to just use it by default:

# Enable Pretty Printing for stdout
import pprint
def my_displayhook(value):
    if value is not None:
            import __builtin__
            __builtin__._ = value
        except ImportError:
            __builtins__._ = value
sys.displayhook = my_displayhook

It is also very useful to be able to load up your favorite editor to edit lines of code from the interpreter, you can do this by adding the following into your ~/

import os
import sys
from code import InteractiveConsole
from tempfile import mkstemp
EDITOR = os.environ.get('EDITOR', 'vi')
EDIT_CMD = '\e'
class EditableBufferInteractiveConsole(InteractiveConsole):
    def __init__(self, *args, **kwargs):
        self.last_buffer = [] # This holds the last executed statement
        InteractiveConsole.__init__(self, *args, **kwargs)
    def runsource(self, source, *args):
        self.last_buffer = [ source.encode('latin-1') ]
        return InteractiveConsole.runsource(self, source, *args)
    def raw_input(self, *args):
        line = InteractiveConsole.raw_input(self, *args)
        if line == EDIT_CMD:
            fd, tmpfl = mkstemp('.py')
            os.write(fd, b'\n'.join(self.last_buffer))
            os.system('%s %s' % (EDITOR, tmpfl))
            line = open(tmpfl).read()
            tmpfl = ''
            lines = line.split( '\n' )
            for i in range(len(lines) - 1): self.push( lines[i] )
            line = lines[-1]
        return line
c = EditableBufferInteractiveConsole(locals=locals())
# Exit the Python shell on exiting the InteractiveConsole

For Django developers when you load up the ./ shell it is nice to have access to all your models and settings for testing:

# If we're working with a Django project, set up the environment
if 'DJANGO_SETTINGS_MODULE' in os.environ:
    from django.db.models.loading import get_models
    from django.test.client import Client
    from django.test.utils import setup_test_environment, teardown_test_environment
    from django.conf import settings as S
    class DjangoModels(object):
        """Loop through all the models in INSTALLED_APPS and import them."""
        def __init__(self):
            for m in get_models():
                setattr(self, m.__name__, m)
    A = DjangoModels()
    C = Client()

After these tweaks the python interpreter is a lot more powerful and you really lose the need for the more interactive shells like ipython and bpython. All of these settings work in both python2 and python3.

If you want to see my complete ~/ you can get it on github