Error handling when importing modules

Question

This probably has an obvious answer, but I\'m a beginner. I\'ve got a \"module\" (really just a file with a bunch of functions I often use) at the beginning of which I impo

Answer 1

I don't think try except block is un-pythonic; instead it's a common way to handle import on Python.

Quoting Dive into Python:

There are a lot of other uses for exceptions besides handling actual error conditions. A common use in the standard Python library is to try to import a module, and then check whether it worked. Importing a module that does not exist will raise an ImportError exception. You can use this to define multiple levels of functionality based on which modules are available at run-time, or to support multiple platforms (where platform-specific code is separated into different modules).

The next example demonstrates how to use an exception to support platform-specific functionality.

try:
    import termios, TERMIOS                     
except ImportError:
    try:
        import msvcrt                           
    except ImportError:
        try:
            from EasyDialogs import AskPassword 
        except ImportError:
            getpass = default_getpass           
        else:                                   
            getpass = AskPassword
    else:
        getpass = win_getpass
else:
    getpass = unix_getpass

Answer 2

The easiest way is to ensure that all modules can be loaded on all systems. If that doesn't work, enclosing each import statement in a try block is the next best solution and not un-Pythonic at all.

Answer 3

As advocated by https://stackoverflow.com/a/20228312/1587329 [modified, with an edit from @Ian]

from importlib import import_module

named_libs = [('numpy', 'np'), ('matplotlib', 'mp')] # (library_name, shorthand)
for (name, short) in named_libs:
    try:
        lib = import_module(name)
    except:
        print sys.exc_info()
    else:
        globals()[short] = lib

imports all libraries in named_libs. The first string is the library name, the second the shorthand. For unnamed libraries, you can use the original:

from importlib import import_module     

libnames = ['numpy', 'scipy', 'operator']
for libname in libnames:
    try:
        lib = import_module(libname)
    except:
        print sys.exc_info()
    else:
        globals()[libname] = lib