How to check if a module is installed in Python and, if not, install it within the code?

EDIT - 2020/02/03

The pip module has updated quite a lot since the time I posted this answer. I've updated the snippet with the proper way to install a missing dependency, which is to use subprocess and pkg_resources, and not pip.

To hide the output, you can redirect the subprocess output to devnull:

import sys
import subprocess
import pkg_resources

required = {'mutagen', 'gTTS'}
installed = {pkg.key for pkg in pkg_resources.working_set}
missing = required - installed

if missing:
    python = sys.executable
    subprocess.check_call([python, '-m', 'pip', 'install', *missing], stdout=subprocess.DEVNULL)

Like @zwer mentioned, the above works, although it is not seen as a proper way of packaging your project. To look at this in better depth, read the the page How to package a Python App.

you can use try/except:

try:
    import time
    print("module 'time' is installed")
except ModuleNotFoundError:
    print("module 'time' is not installed")
    # or
    install("time") # the install function from the question

If you want to know if a package installed, you can check it in your terminal using the next command:

pip list | grep <module_name_you_want_to_check>

How this works:

pip list

lists all modules installed in your Python.

The vertical bar | is commonly referred to as a "pipe". It is used to pipe one command into another. That is, it directs the output from the first command into the input for the second command.

grep <module_name_you_want_to_check>

find the keyword from the list.

Example:

pip list| grep quant

Lists all packages which start from "quant" (for example "quantstrats"). If you do not have any output, this means the library is not installed.