How to install and import Python modules at runtime?

Question

I want to write a script to automatically setup a brand new ubuntu installation and install a django-based app. Since the script will be run on a new server, the Python scri

Answer 1

You can import pip instead of using subprocess:

import pip

def install(package):
    pip.main(['install', package])

# Example
if __name__ == '__main__':
    try:
        import pexpect
    except ImportError:
        install('pexpect')
        import pexpect

Another take:

import pip

def import_with_auto_install(package):
    try:
        return __import__(package)
    except ImportError:
        pip.main(['install', package])
    return __import__(package)

# Example
if __name__ == '__main__':
    pexpect = import_with_auto_install('pexpect')
    print(pexpect)

[edit]

You should consider using a requirements.txt along with pip. Seems like you are trying to automate deployments (and this is good!), in my tool belt I have also virtualenvwrapper, vagrant and ansible.

This is the output for me:

(test)root@vagrant:~/test# pip uninstall pexpect
Uninstalling pexpect:
  /usr/lib/python-environments/test/lib/python2.6/site-packages/ANSI.py
  /usr/lib/python-environments/test/lib/python2.6/site-packages/ANSI.pyc
  /usr/lib/python-environments/test/lib/python2.6/site-packages/FSM.py
  /usr/lib/python-environments/test/lib/python2.6/site-packages/FSM.pyc
  /usr/lib/python-environments/test/lib/python2.6/site-packages/fdpexpect.py
  /usr/lib/python-environments/test/lib/python2.6/site-packages/fdpexpect.pyc
  /usr/lib/python-environments/test/lib/python2.6/site-packages/pexpect-2.4-py2.6.egg-info
  /usr/lib/python-environments/test/lib/python2.6/site-packages/pexpect.py
  /usr/lib/python-environments/test/lib/python2.6/site-packages/pexpect.pyc
  /usr/lib/python-environments/test/lib/python2.6/site-packages/pxssh.py
  /usr/lib/python-environments/test/lib/python2.6/site-packages/pxssh.pyc
  /usr/lib/python-environments/test/lib/python2.6/site-packages/screen.py
  /usr/lib/python-environments/test/lib/python2.6/site-packages/screen.pyc
Proceed (y/n)? y
  Successfully uninstalled pexpect
(test)root@vagrant:~/test# python test.py
Downloading/unpacking pexpect
  Downloading pexpect-2.4.tar.gz (113Kb): 113Kb downloaded
  Running setup.py egg_info for package pexpect
Installing collected packages: pexpect
  Running setup.py install for pexpect
Successfully installed pexpect
Cleaning up...

(test)root@vagrant:~/test#