fix bug in module reload

[KaitoHH]

This fixed #149.

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Problem

I encountered a module-import error.
For example, if I create a project like this:

# Project: f_project
def f():
    print('f called.')

and in another project, I import f_project and call f() like this:

...
# Project: spider
from projects.f_project import f

class...
    def on_start(self):
        f() # this calls f in f_project
        ...
...

It will output the correct result the first time you run the script, but when you modify the script in f_project, for example, change f called to f called again, and run spider again, you will still get the result as it was. However, restarting pyspider can reload the project.

Analysis

After reading code in \pyspider\processor\project_module.py, I think this bug was produced because pyspider use six.exec_(code, mod.__dict__) to dynamically execute the script, and this code import a same module multiple times whenever pressing the run button. Since in Python, a module can only be imported once, any import after the first import will be ignored, so the result remains the same.

Solution

I'm willing to use something like six.moves.reload_module to reload the module, but it has no effect, so I just simply removed all modules matching projects.* (that means all modules in pyspider project) before ProjectLoader.load_module was called. As a result, all modules in this project will be re-import, and that solved the problem.

Looking forward to any better solution on solving this bug if available.