The xargs solution works but can have portability issues (BSD/GNU) and/or be cumbersome if you have comments or blank lines in your requirements file.

As for the usecase where such a behavior would be required, I use for instance two separate requirement files, one which is only listing core dependencies that need to be always installed and another file with non-core dependencies that are in 90% of the cases not needed for most usecases. That would be an equivalent of the Recommends section of a debian package.

I use the following shell script (requires sed) to install optional dependencies:

#!/bin/sh

while read dependency; do
    dependency_stripped="$(echo "${dependency}" | sed -e 's/^[[:space:]]*//' -e 's/[[:space:]]*$//')"
    # Skip comments
    if [[ $dependency_stripped == #* ]]; then
        continue
    # Skip blank lines
    elif [ -z "$dependency_stripped" ]; then
        continue
    else
        if pip install "$dependency_stripped"; then
            echo "$dependency_stripped is installed"
        else
            echo "Could not install $dependency_stripped, skipping"
        fi
    fi
done < recommends.txt

For Windows:

pip version >=18

import sys
from pip._internal import main as pip_main

def install(package):
    pip_main(['install', package])

if __name__ == '__main__':
    with open(sys.argv[1]) as f:
        for line in f:
            install(line)

pip version <18

import sys
import pip

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

if __name__ == '__main__':
    with open(sys.argv[1]) as f:
        for line in f:
            install(line)

Thanks, Etienne Prothon for windows cases.

But, after upgrading to pip 18, pip package don’t expose main to public. So you may need to change code like this.

 # This code install line by line a list of pip package 
 import sys
 from pip._internal import main as pip_main

 def install(package):
    pip_main(['install', package])

 if __name__ == '__main__':
    with open(sys.argv[1]) as f:
        for line in f:
            install(line)

This solution handles empty lines, whitespace lines, # comment lines, whitespace-then-# comment lines in your requirements.txt.

cat requirements.txt | sed -e '/^s*#.*$/d' -e '/^s*$/d' | xargs -n 1 pip install

Hat tip to this answer for the sed magic.

For Windows:

import os
from pip.__main__ import _main as main

error_log = open('error_log.txt', 'w')

def install(package):
    try:
        main(['install'] + [str(package)])
    except Exception as e:
        error_log.write(str(e))

if __name__ == '__main__':
    f = open('requirements1.txt', 'r')
    for line in f:
        install(line)
    f.close()
    error_log.close()

1. Create a local directory, and put your requirements.txt file in it.
2. Copy the code above and save it as a python file in the same directory. Remember to use .py extension, for instance, install_packages.py
3. Run this file using a cmd: python install_packages.py
4. All the packages mentioned will be installed in one go without stopping at all. 🙂

You can add other parameters in install function. Like:
main(['install'] + [str(package)] + ['--update'])

For windows users, you can use this:

FOR /F %k in (requirements.txt) DO ( if NOT # == %k ( pip install %k ) )

Logic: for every dependency in file(requirements.txt), install them and ignore those start with "#".

For Windows using PowerShell:

foreach($line in Get-Content requirements.txt) {
    if(!($line.StartsWith('#'))){
        pip install $line
    }
}

One line PowerShell:

Get-Content .requirements.txt | ForEach-Object {pip install $_}

If you need to ignore certain lines then:

Get-Content .requirements.txt | ForEach-Object {if (!$_.startswith("#")){pip install $_}}

OR

Get-Content .requirements.txt | ForEach-Object {if ($_ -notmatch "#"){pip install $_}}

Building on the answer by @MZD, here’s a solution to filter out all text starting with a comment sign #

cat requirements.txt | grep -Eo '(^[^#]+)' | xargs -n 1 pip install

Another option is to use pip install --dry-run to get a list of packages that you need to install and then keep trying it and remove the ones that don’t work.

A very general solution

The following code installs all requirements for:

• multiple requirement files (requirements1.txt, requirements2.txt)
• ignores lines with comments #
• skips packages, which are not instalable
• runs pip install each line (not each word as in some other answers)

$ (cat requirements1.txt; echo ""; cat requirements2.txt) | grep "^[^#]" | xargs -L 1 pip install