import module from string variable

Question

I'm working on a documentation (personal) for nested matplotlib (MPL) library, which differs from MPL own provided, by interested submodule packages. I'm writing Python script which I hope will automate document generation from future MPL releases.
I selected interested submodules/packages and want to list their main classes from which I'll generate list and process it with pydoc

Problem is that I can't find a way to instruct Python to load submodule from string. Here is example of what I tried:

import matplotlib.text as text
x = dir(text)

.

i = __import__('matplotlib.text')
y = dir(i)

.

j = __import__('matplotlib')
z = dir(j)

And here is 3 way comparison of above lists through pprint:

I don't understand what's loaded in y object - it's base matplotlib plus something else, but it lack information that I wanted and that is main classes from matplotlib.text package. It's top blue coloured part on screenshot (x list)

Please don't suggest Sphinx as different approach.

Answer 1

importlib.import_module is what you are looking for. It returns the imported module.

import importlib

mymodule = importlib.import_module('matplotlib.text')

You can thereafter access anything in the module as mymodule.myclass, mymodule.myfunction, etc.

Answer 2

spent some time trying to import modules from a list, and this is the thread that got me most of the way there - but I didnt grasp the use of ___import____ -

so here's how to import a module from a string, and get the same behavior as just import. And try/except the error case, too. :)

  pipmodules = ['pycurl', 'ansible', 'bad_module_no_beer']
  for module in pipmodules:
      try:
          # because we want to import using a variable, do it this way
          module_obj = __import__(module)
          # create a global object containging our module
          globals()[module] = module_obj
      except ImportError:
          sys.stderr.write("ERROR: missing python module: " + module + "\n")
          sys.exit(1)

and yes, for python 2.7> you have other options - but for 2.6<, this works.

Answer 3

Apart from using the importlib one can also use exec method to import a module from a string variable.

Here I am showing an example of importing the combinations method from itertools package using the exec method:

MODULES = [
    ['itertools','combinations'],
]

for ITEM in MODULES:
    import_str = "from {0} import {1}".format(ITEM[0],', '.join(str(i) for i in ITEM[1:]))
    exec(import_str)

ar = list(combinations([1, 2, 3, 4], 2))
for elements in ar:
    print(elements)

Output:

(1, 2)
(1, 3)
(1, 4)
(2, 3)
(2, 4)
(3, 4)

Answer 4

I developed these 3 useful functions:

def loadModule(moduleName):
    module = None
    try:
        import sys
        del sys.modules[moduleName]
    except BaseException as err:
        pass
    try:
        import importlib
        module = importlib.import_module(moduleName)
    except BaseException as err:
        serr = str(err)
        print("Error to load the module '" + moduleName + "': " + serr)
    return module

def reloadModule(moduleName):
    module = loadModule(moduleName)
    moduleName, modulePath = str(module).replace("' from '", "||").replace("<module '", '').replace("'>", '').split("||")
    if (modulePath.endswith(".pyc")):
        import os
        os.remove(modulePath)
        module = loadModule(moduleName)
    return module

def getInstance(moduleName, param1, param2, param3):
    module = reloadModule(moduleName)
    instance = eval("module." + moduleName + "(param1, param2, param3)")
    return instance

And everytime I want to reload a new instance I just have to call getInstance() like this:

myInstance = getInstance("MyModule", myParam1, myParam2, myParam3)

Finally I can call all the functions inside the new Instance:

myInstance.aFunction()

The only specificity here is to customize the params list (param1, param2, param3) of your instance.

Answer 5

Module auto-install & import from list

Below script works fine with both submodules and pseudo submodules.

# PyPI imports
import pkg_resources, subprocess, sys

modules   = {'lxml.etree', 'pandas', 'screeninfo'}
required  = {m.split('.')[0] for m in modules}
installed = {pkg.key for pkg in pkg_resources.working_set}
missing   = required - installed

if missing:
    subprocess.check_call([sys.executable, '-m', 'pip', 'install', '--upgrade', 'pip'])
    subprocess.check_call([sys.executable, '-m', 'pip', 'install', *missing])

for module in set.union(required, modules):
    globals()[module] = __import__(module)

Tests:

print(pandas.__version__)
print(lxml.etree.LXML_VERSION)