Check if Python Package is installed

Question

What s a good way to check if a package is installed while within a Python script  I know it s easy from the interpreter  but I need to do it within a script    I guess I could check if there s a directory on the system that s created during the installation  but I feel like there s a better way  I m trying to make sure the Skype4Py package is installed  and if not I ll install it   My ideas for accomplishing the check   check for a directory in the typical install path try to import the package and if an exception is throw  then install package

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A quick way is to use python command line tool  Simply type import  lt your module name gt  You see an error if module is missing     python Python 2 7 6  default  Jun 22 2015  17 58 13    gt  gt  gt  import sys  gt  gt  gt  import jocker Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  ImportError  No module named jocker

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I d like to add some thoughts findings of mine to this topic  I m writing a script that checks all requirements for a custom made program  There are many checks with python modules too    There s a little issue with the   try     import    except          solution   In my case one of the python modules called python-nmap  but you import it with import nmap and as you see the names mismatch  Therefore the test with the above solution returns a False result  and it also imports the module on hit  but maybe no need to use a lot of memory for a simple test check   I also found that   import pip installed packages   pip get installed distributions     installed packages will have only the packages has been installed with pip  On my system pip freeze returns over 40 python modules  while installed packages has only 1  the one I installed manually  python-nmap    Another solution below that I know it may not relevant to the question  but I think it s a good practice to keep the test function separate from the one that performs the install it might be useful for some   The solution that worked for me  It based on this answer How to check if a python module exists without importing it  from imp import find module  def checkPythonmod mod       try          op   find module mod          return True     except ImportError          return False   NOTE  this solution can t find the module by the name python-nmap too  I have to use nmap instead  easy to live with  but in this case the module won t be loaded to the memory whatsoever

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Open your command prompt type  pip3 list

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If you mean a python script  just do something like this  Python 3 3  use sys modules and find spec  import importlib util import sys    For illustrative purposes  name    itertools   if name in sys modules      print f quot  name r  already in sys modules quot   elif  spec    importlib util find spec name   is not None        If you choose to perform the actual import         module   importlib util module from spec spec      sys modules name    module     spec loader exec module module      print f quot  name r  has been imported quot   else      print f quot can t find the  name r  module quot    Python 3  try      import mymodule except ImportError as e      pass    module doesn t exist  deal with it   Python 2  try      import mymodule except ImportError  e      pass    module doesn t exist  deal with it

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if pip list   grep -q    PACKAGENAME s      installed     else     not installed     fi

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Go option  2   If ImportError is thrown  then the package is not installed  or not in sys path

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If you d like your script to install missing packages and continue  you could do something like this  on example of  krbV  module in  python-krbV  package    import pip import sys  for m  pkg in    krbV    python-krbV         try          setattr sys modules   name     m    import   m       except ImportError          pip main   install   pkg           setattr sys modules   name     m    import   m

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If you want to have the check from the terminal  you can run  pip3 show package name   and if nothing is returned  the package is not installed   If perhaps you want to automate this check  so that for example you can install it if missing  you can have the following in your bash script   pip3 show package name 1 gt  dev null  pip for Python 2 if         0    then    echo  Installed   Replace with your actions else    echo  Not Installed   Replace with your actions   pip3 install --upgrade package name    fi

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In the Terminal type  pip show some package name   Example  pip show matplotlib

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Hmmm     the closest I saw to a convenient answer was using the command line to try the import  But I prefer to even avoid that   How about  pip freeze   grep pkgname   I tried it and it works well  It also shows you the version it has and whether it is installed under version control  install  or editable  develop

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Is there any chance to use the snippets given below  When I run this code  it returns  quot module  pandas  is not installed quot  a    quot pandas quot   try      import a     print  quot module  quot  a  quot  is installed quot   except ModuleNotFoundError      print  quot module  quot  a  quot  is not installed quot    But when I run the code given below  try      import pandas     print  quot module is installed quot   except ModuleNotFoundError      print  quot module is not installed quot    It returns  quot module pandas is installed quot   What is the difference between them

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I would like to comment to  ice nicer reply but I cannot  so     My observations is that packages with dashes are saved with underscores  not only with dots as pointed out by  dwich comment  For example  you do pip3 install sphinx-rtd-theme  but    importlib util find spec sphinx rtd theme  returns an Object importlib util find spec sphinx-rtd-theme  returns None importlib util find spec sphinx rtd theme  raises ModuleNotFoundError   Moreover  some names are totally changed   For example  you do pip3 install pyyaml but it is saved simply as yaml  I am using python3 8

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You can use this  class myError exception    pass   Or do some thing like this  try   import mymodule except ImportError as e   raise myError  quot error was occurred quot

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As an extension of this answer   For Python 2    pip show  lt package name gt  will perform the same task   For example pip show numpy will return the following or alike   Name  numpy Version  1 11 1 Summary  NumPy  array processing for numbers  strings  records  and objects  Home-page  http   www numpy org Author  NumPy Developers Author-email  numpy-discussion scipy org License  BSD Location   home     anaconda2 lib python2 7 site-packages Requires   Required-by  smop  pandas  tables  spectrum  seaborn  patsy  odo  numpy-stl  numba  nfft  netCDF4  MDAnalysis  matplotlib  h5py  GridDataFormats  dynd  datashape  Bottleneck  blaze  astropy

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Updated answer  A better way of doing this is   import subprocess import sys  reqs   subprocess check output  sys executable   -m    pip    freeze    installed packages    r decode   split       0  for r in reqs split      The result   print installed packages          Django        six        requests       Check if requests is installed   if  requests  in installed packages        Do something   Why this way  Sometimes you have app name collisions  Importing from the app namespace doesn t give you the full picture of what s installed on the system   Note  that proposed solution works    When using pip to install from PyPI or from any other alternative source  like pip install http   some site package-name zip or any other archive type    When installing manually using python setup py install   When installing from system repositories  like sudo apt install python-requests     Cases when it might not work    When installing in development mode  like python setup py develop  When installing in development mode  like pip install -e  path to package source     Old answer  A better way of doing this is   import pip installed packages   pip get installed distributions     For pip  10 x use   from pip  internal utils misc import get installed distributions   Why this way  Sometimes you have app name collisions  Importing from the app namespace doesn t give you the full picture of what s installed on the system   As a result  you get a list of pkg resources Distribution objects  See the following as an example   print installed packages        Django 1 6 4   path-to-your-env lib python2 7 site-packages         six 1 6 1   path-to-your-env lib python2 7 site-packages         requests 2 5 0   path-to-your-env lib python2 7 site-packages        Make a list of it   flat installed packages    package project name for package in installed packages          Django        six        requests       Check if requests is installed   if  requests  in flat installed packages        Do something

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You can use the pkg resources module from setuptools  For example   import pkg resources  package name    cool package  try      cool package dist info   pkg resources get distribution package name  except pkg resources DistributionNotFound      print     not installed  format package name   else      print cool package dist info    Note that there is a difference between python module and a python package  A package can contain multiple modules and module s names might not match the package name

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As of Python 3 3  you can use the find spec   method  import importlib util    For illustrative purposes  package name    pandas   spec   importlib util find spec package name  if spec is None      print package name    is not installed

[python] Check if Python Package is installed

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