mjhjmtu

Need to verify whether it is installed or not before the program can run.

Type in the shell: pydoc modules .

This will list modules and you can grep the module which you want.

Found on stackoverflow here

You should use pip's list command with grep, that only lists installed packages (not all modules and their neighbours as well):

pip list | grep -F package_name

If the package doesn't do something crazy or time consuming on import you can try actually importing it:

if python -c "import package_name" &> /dev/null; then
 echo 'all good'
else
 echo 'uh oh'
fi

I have found existing answers incomplete and lacking good enough examples. Here is the solution I have settled on:

# an example checking if the pandas package is installed
if python -c 'import pkgutil; exit(not pkgutil.find_loader("pandas"))'; then
 echo 'pandas found'
else
 echo 'pandas not found'
fi

A Github gist of this example can be found here: https://gist.github.com/shaypal5/d505af9953cd86f59c750fa600ee4ba6

I used a slightly stricter version of Anthon's answer, for use in a script:

pip3 list |
 grep -v "^Package *Version$" | grep -v "^-*$" |
 cut -d ' ' -f 1 |
 grep -xF "$package_name"

The first two greps are intended to strip the header lines from pip3's output.

The cut then selects only the package names (discarding the version numbers).

Then the final grep can perform an exact search for the relevant $package_name

If the package is found, it will display the package name, and return with exit code 0. If you don't want to see the package name, end the command with >/dev/null

You can also use something like this in your scripts.

python -c "import sys, pkgutil; sys.exit(0 if pkgutil.find_loader('$Package') else 1)"

What you'd get when a package is not installed.

Package=psutil
python3 -c "import sys, pkgutil; sys.exit(0 if pkgutil.find_loader('$Package') else 1)"
echo $?
1

What you'd get when a package is installed.

Package=requests
python3 -c "import sys, pkgutil; sys.exit(0 if pkgutil.find_loader('$Package') else 1)"
echo $?
0

Works in python2 and python3, and then you install based on the exit code.