Python: AttributeError: 'module' object has no attribute 'append'

Question

I'm trying to make an engine that takes the contents of a file that has python files and functions within them in a format as follows:

lib1 func1 func2 func3
lib2 func4

etc. I set up a test with two python files and three functions, but the code I am using to import the libraries and functions isn't working:

class engine (object):
    def __init__ (self, sceneFile):
        # gets contents of sceneFile, then closes
        scenes         = open (sceneFile, 'r')
        lines = scenes.readlines ()
        scenes.close ()
        self.libs = []

        # finds functions and libraries
        for i in range (len (lines)):
            lineContents = lines[i].split()
            self.libs.append (importlib.import_module (lineContents[0]))  # libraries in sceneFile
            for j in range (len (lineContents) - 1):
                self.libs[i].append (lineContents[j + 1])          # functions in sceneFile

    def start (self, nextScene):
        # finds function and library, imports
        for i in range (len (self.libs)):
            for j in range (len (self.libs[i])):
                if self.libs[i][j] == nextScene:
                    nextScene = getattr (self.libs[i], self.libs[i][j])
                    self.start (nextScene)

When I try running this with the test programs, this error pops up:

Traceback (most recent call last):
  File "ugsE.py", line 32, in <module>
    Engine = engine ("ugsEtest.txt")
  File "ugsE.py", line 21, in __init__
    self.libs[i].append (lineContents[j + 1])          # functions in sceneFile
AttributeError: 'module' object has no attribute 'append'

What does this mean? I have a feeling that it's because I'm creating a list of modules, but shouldn't that work?

Answer 1

libs is a list of modules, so libs[i] is a module. libs[i].append fails because you can't append something to a module.

Strictly, this code will actually run in the unlikely case that libs[i] is a module that exposes its own append method (with a compatible signature), but this certainly won't do what you want.

---

You could achieve what you want by turning libs into a list of tuples, where the first element is the library and the second is a list of functions associated with that library:

for line in lines:
    lineContents = line.split()
    self.libs.append((importlib.import_module(lineContents[0]), lineContents[1:]))

Then you can access library i as self.libs[i][0] and function j as self.libs[i][1][j] .

If you want, you can also eliminate the loop and reduce the whole of __init__ to just three lines using slices , list comprehensions , and a with statement :

with open(sceneFile, 'r') as scenes:
    lines = (l.split() for l in scenes)
    self.libs = [(importlib.import_module(l[0]), l[1:]) for l in lines]

Answer 2

libs looks like an element of the array. Unless you can guarantee self.libs[i] is itself an attay it won't have an append method.

If you want to 'append' at an index, use insert(i, x)