在Python库中动态加载模块的最佳方法

Question

EDIT: Turns out the problem has to do with the path.

If I cd into the directory containing the library and run python __init__.py the imports all work fine. It's if I'm in a different directory and try to import the library itself (ie in the parent directory, and trying to import) that the failure occurs.

I don't see any way to literally specify a path for an import statement.

So, I'm wondering if the best way is just to add the directory in scriptDir to the sys.path? Is this the best way to do it? I feel like there should be a more elegant method, but...

---

I want to write a library that I will be able to extend very easily.

Here's some skeleton/pseudo code for what I want to do. In reality this code is a lot more complex, but it follows the basic premise - import each file, check it, and determine if we should use it; then allocate it into a list of module references. All of this would be contained in a single library folder.

I want the library, when imported, to dynamically import any file found in its directory starting with "plugin_". See the code:

init .py:

import os.path

scriptDir = os.path.dirname(__file__)
mods = []
thisMod = 0

for file in os.listdir(scriptDir):
    if (file[0:7] == "plugin_" and file[-3:] == ".py"):
        thisMod = __import__(".".join(file.split(".")[0:-1]))
        print "debug: imported %s" % thisMod.modName
        if (thisMod.enable == True):
            mods.append(thisMod)
        else:
            print "debug: not loading %s because it's disabled." % thisMod.modName

def listMods():
    "This function should print the names of all loaded modules."
    for m in mods:
        print "debug: module %s" % m.modName

def runMods():
    "This function should execute the run method for ALL modules."
    for m in mods:
        c = m.ModuleClass()
        c.run()

def selectMod(modNum):
    "This function should let us select a single module for the runSelectedMod function."
    thisMod = mods[modNum]

def runSelectedMod():
    "This function should run the 'run' method for ONLY the previously selected module."
    if (thisMod == 0):
        raise ArgumentError("you didn't assign a module yet.")
    c = thisMod.ModuleClass()
    c.run()

plugin_test1.py

modName = "test module 1"
enable = True
class ModuleClass:
    def run(self):
        print "test module 1 is running"

plugin_math.py

modName = "math module"
enable = True
class ModuleClass:
    def run(self):
        print "mathematical result: %d" % (1+1)

plugin_bad.py

modName = "bad module"
enable = False
class ModuleClass:
    def __init__(self):
        print "x"[4] # throws IndexError, this code should not run.
    def run(self):
        print "divide by zero: %f" % (5 / 0) # this code should not run.

The problem I've already found is import won't work since I'm not importing whole libraries, but rather individual files. I'm guessing there is either an alternate syntax to import for this purpose? For example, import plugin_test and from plugin_math import ModuleClass work but my use of import isn't. I get an error:

thisMod = __import__(".".join(file.split(".")[0:-1]))
ImportError: No module named plugin_test1

Now, another question is: How will this end up working if I use py2exe, py2app, etc. to compile this into a compact library? If I recall, don't these apps compress all the local libraries into a site_packages.zip file?...

I'm still learning how to do this type of advanced coding in Python, so any advice is appreciated.

Thanks!

Answer 1

I was able to run it in Python 3. The only change not regarding syntax is the scriptDir :

import os.path

scriptDir = os.path.dirname(os.path.abspath(__file__))
mods = []
thisMod = 0

for file in os.listdir(scriptDir):
    if (file[0:7] == "plugin_" and file[-3:] == ".py"):
        thisMod = __import__(".".join(file.split(".")[0:-1]))
        print ("debug: imported %s" % thisMod.modName)
        if (thisMod.enable == True):
            mods.append(thisMod)
        else:
            print ("debug: not loading %s because it's disabled." % thisMod.modName)

def listMods():
    "This function should print the names of all loaded modules."
    for m in mods:
        print ("debug: module %s" % m.modName)

def runMods():
    "This function should execute the run method for ALL modules."
    for m in mods:
        c = m.ModuleClass()
        c.run()

def selectMod(modNum):
    "This function should let us select a single module for the runSelectedMod function."
    thisMod = mods[modNum]

def runSelectedMod():
    "This function should run the 'run' method for ONLY the previously selected module."
    if (thisMod == 0):
        raise ArgumentError("you didn't assign a module yet.")
    c = thisMod.ModuleClass()
    c.run()

gives:

C:\Users\mm\Desktop\ING.SW\python>python so\dina.py
debug: imported bad module
debug: not loading bad module because it's disabled.
debug: imported math module
debug: imported test module 1

I guess you have a different problem, since the file name is actually read (as it's printed in the error message), but still...