Installing packages from a list using pip

问题:

I am trying to install a list of packages using pip.

The code which I used is:

import pip

def install(package_name):
        try:
            pip.main(['install', package_name])
        except:
            print("Unable to install " + package_name)

This code works fine and if a package is not available, it gives an error:

No matching distributions found

However, what I am trying to do is if an installation fails (for eg: invalid package name), I want to print the package which failed.

What can be done for that?

Any help would be appreciated, thank you.

回答1:

Try checking the return value for non-zero, which indicates an error occurred with the install. Not all errors trigger exceptions.

import pip

def install(package_name):
        try:
            pipcode = pip.main(['install', package_name])
            if pipcode != 0:
                print("Unable to install " + package_name + " ; pipcode %d" % pipcode)
        except:
            print("Unable to install " + package_name)

回答2:

You can check the value of package to verify if no matching distribution was find. Normally the package will return 0 if exists a installation candidate, otherwise will return 1 for no candidate found

import pip

def install(package_name):
    package = pip.main(['install', package_name])      
    result = "Package successfully installed: " if package == 0 else "Unable to find package: "
    print(result + package_name)

So, if you try to do something like this:

>>> install("Virtualenvs")

Will return:

Collecting virtualenvs
Could not find a version that satisfies the requirement virtualenvs (from versions: )
No matching distribution found for virtualenvs
Unable to find package: virtualenvs

Because there's no valid package for "Birtualenvs". But with a valid package:

>>> install("virtualenv")

Will return:

Requirement already satisfied: virtualenv in/usr/lib/python2.7/dist-packages
Package successfully installed: virtualenv