I am installing packages from requirements.txt

pip install -r requirements.txt

The requirements.txt file reads:

Pillow
lxml
cssselect
jieba
beautifulsoup
nltk

lxml is the only package failing to install and this leads to everything failing (expected results as pointed out by larsks in the comments). However, after lxml fails pip still runs through and downloads the rest of the packages.

From what I understand the pip install -r requirements.txt command will fail if any of the packages listed in the requirements.txt fail to install.

Is there any argument I can pass when running pip install -r requirements.txt to tell it to install what it can and skip the packages that it cannot, or to exit as soon as it sees something fail?

Running each line with pip install may be a workaround.

cat requirements.txt | xargs -n 1 pip install

Note: -a parameter is not available under MacOS, so old cat is more portable.

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:

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)

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

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)

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'])