how to make import conditionally in Python?

Question

I want to do something like this in C:

#ifdef SOMETHING
do_this();
#endif

But in Python this doesn't jive:

if something:
    import module

What am I doing wrong? Is this possible in the first place?

Answer 1

It should work fine:

>>> if False:
...     import sys
... 
>>> sys
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'sys' is not defined
>>> if True:
...     import sys
... 
>>> sys
<module 'sys' (built-in)>

Answer 2

In Python there's a built-in feature called "Exception".. Applying to your needs:

try:

    import <module>

except:     #Catches every error
    raise   #and print error

There are more complex structures so search on the web for more documentation.

Answer 3

If you're getting this:

NameError: name 'something' is not defined

then the problem here is not with the import statement but with the use of something, a variable you apparently haven't initialized. Just make sure it's initialized to either True or False, and it'll work.

Answer 4

In the C construct, the conditional define #ifdef tests whether "SOMETHING" exists only, where your python expression tests whether the value of the expression is either True or False, in my opinion two very different things, in addition, the C construct is evaluated at compile time.

"something" based in your original question must be a variable or expression that (exists and) evaluates to true or false, as other people already pointed out, the problem may be with that "something" variable not being defined. so the "closest equivalent" in python would be something like:

if 'something' in locals(): # or you can use globals(), depends on your context
    import module

or (hacky):

try:
    something
    import module
except NameError, ImportError:
    pass # or add code to handle the exception

hth