Python dependencies importing

Question

Suppose I use some 3rd party module that depends on code from another one:

# third_party.py
from package import fun, A

class B(A):
    def foo(self):
        self.do()
        self.some()
        self.stuff()
        return fun(self)

And then I want to inherit this class in my code to change functionality:

# my_code.py

from third_party import B

# from third_party import fun?
# from package import fun?

class C(B):
    def foo(self):
        return fun(self)

What is better: from package import fun or from third_party import fun to get access to fun?

I like second variant since I may do not bother with actual paths and import all dependences from third_party package, but has this way any drawbacks? Is this a good or bad practice?

Thanks!

Constantinius · Accepted Answer · 2012-10-30 10:36:18Z

I dont't think that importing a function/class from a third party package is a bad practice, it may even has some benefits (e.g: If you want to monkey patch a package, or need to be sure, that something is set up correctly).

It even may be necessary to support a variety of setups. Consider the ElementTree API, which is differently available on specific Python versions and may even be provided from third party libraries (taken from here):

# somepackage.py

try:
  from lxml import etree
  print("running with lxml.etree")
except ImportError:
  try:
    # Python 2.5
    import xml.etree.cElementTree as etree
    print("running with cElementTree on Python 2.5+")
  except ImportError:
    try:
      # Python 2.5
      import xml.etree.ElementTree as etree
      print("running with ElementTree on Python 2.5+")
    except ImportError:
      try:
        # normal cElementTree install
        import cElementTree as etree
        print("running with cElementTree")
      except ImportError:
        try:
          # normal ElementTree install
          import elementtree.ElementTree as etree
          print("running with ElementTree")
        except ImportError:
          print("Failed to import ElementTree from any known place")

Now, it is guranteed that somepackage contains a working etree implementation, even on different Python installations and your package serves as an abstraction.

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