Some Statements on Modules and Packages

Modules contain definitions (of functions and variables) and statements. They organize namespaces.
Modules have their private symbol table which acts as the global symbol table for all functions inside the module.

Modules correspond to Python files.

 
#!/bin/env python
"""
global doc string
"""
def f1():
    var = 1
    return 

class myClass:
    """ myClass doc string """
    a = 1
    def memFunc(self):
        pass

def main():
    print( "myClass.__dict__ %s " % myClass.__dict__)
    print( "globals: %s" % str( globals()))
    return

if __name__ == "__main__":
    main()

Output: 

myClass.__dict__ {'a': 1, '__module__': '__main__', '__doc__': ' myClass doc string ', 
                  'memFunc': <function memFunc at 0x7fd7cf4af6e0>} 
globals: {'f1': <function f1 at 0x7fd7cf4af5f0>, 
           '__builtins__': <module '__builtin__' (built-in)>, 
           '__file__': 't1.py', '__package__': None, 
           'myClass': <class __main__.myClass at 0x7fd7cf49d6d0>, 
           '__name__': '__main__', 
           'main': <function main at 0x7fd7cf4af668>, '__doc__': '\nglobal doc string\n'}

If a module is executed as a script, the __name__ variable is set to __main__:
```
if __name__ == "__main__":
    modMain()
```
Packages organize modules.
A directory containing an __init__ file is a package.
The __init__ file can be empty, but it can also be used to populate the package name space by import startments.
The following example demonstrates the effects of imports of sub-packages:
```
 
  PySpectra/__init__.py contains
     from pqtgrph.graphics import *
  
  and PySpectra/pqtgrph/graphics.py contains
    import PySpectra.misc.zmqIfc as zmqIfc
```
As a consequence, after import PySpectra the module PySpectra.misc.zmqIfc can be immediately referenced, without further imports.

The list sys.path contains the Python search path. It can be extended at runtime:

 
In [1]: import sys
In [2]: sys.path.insert( 0, "/home/userUser/pythonDir")
In [3]: sys.path
Out[3]: 
['/home/userUser/pythonDir',
 ”,
 '/usr/bin',
 '/usr/lib/python2.7',
...]

The environment variable $PTHONPATH is inserted into sys.path.
Names that are created in a module are called attributes (of the module object).
The module name is stored in __name__.
The function globals() returns a dictionary containing the variables defined in the global name space.
The __dict__ dictionary stores the modules symbol table.
The dir() function returns the modules symbol table.

The built-in variables and functions are in the module __builtin__:

In [4]: import __builtin__

In [5]: dir( __builtin__)
Out[5]: 
['ArithmeticError',
 'AssertionError',
...]