unit4_lesson_01_understanding_modules.py

__author__ = 'Kalyan'

notes = '''
modules are a abstraction feature which greatly aids in building large applications.

modules are defined in .py file (socket.py, random.py, csv.py ...) and usually contain
a set of function, data and class definitions which provide a specific functionality. This
 allows for easy reuse and discovery of functionality. e.g. you can be pretty sure that
 socket module exposes functionality related to communication using sockets.
 
Each of our lesson and assignments is a module too (though they do not expose any useful api).

Reading material:
 - http://effbot.org/zone/import-confusion.htm
'''

notes_1 = '''
All these tests uses module1.py to module4.py. Take a look at them before starting on the tests.
'''

#this is a global import, generally you use only these. rarely will you use function level imports, but we are doing that
#here for the sake of testing how import works by limiting the scope of the import to each function.
import sys

import placeholders
from placeholders import *

def test_module_without_import():
    try:
        module1.greet("jack")
    except NameError as ie :   # what specific exception did you get here, replace ___ with that
        print(ie)    # print it out and see
        assert True

def test_module_usage_needs_import():
    import module1
    assert "module1 says hi to jack" == module1.greet("jack")

def test_module_usage_multiple():
    import module1
    import module2

    assert "module1 says hi to jack" == module1.greet("jack")
    assert "module2 says hi to jack" == module2.greet("jack")

def test_module_import_affects_current_namespace():
    import module1

    def inner_func():
        import module2
        assert True == ('module2' in locals())
        return module2.greet("jack")

    assert "module1 says hi to jack" == module1.greet("jack")
    assert "module2 says hi to jack" == inner_func()

    assert False == ('placeholders' in locals())
    assert True == ('placeholders' in globals())

    assert True == ('module1' in locals())
    assert False == ('module1' in globals())

    assert False == ('module2' in locals())
    assert False == ('module2' in globals())

def test_module_type():
    assert "module" == type(placeholders).__name__

def test_module_is_an_object():
    assert 12 == len(dir(placeholders))
    assert "placeholders" == placeholders.__name__
    assert None == placeholders.__doc__

def test_module_from_import():
    from module1 import greet

    assert False == ('module1' in locals())
    assert True == ('greet' in locals())

    try:
        module1.greet()
    except NameError as ie :
        print(ie)

    assert "module1 says hi to jack" == greet("jack")

def test_module_why_from_import_is_a_bad_idea():
    from module1 import greet
    from module2 import greet

    assert "module2 says hi to jack" == greet("jack")

def test_modules_are_cached():
    import module1
    import module1 as new_name
    def inner():
        import module1
        return module1.some_attr

    try:
        inner()
    except AttributeError as ae: # what exception do you get here?
        print(ae)

    module1.some_attr = 10
    assert 10 == inner()

    def inner2():
        import module1
        return module1.some_attr

    assert 10 == inner2()

    assert "dict" == type(sys.modules).__name__
    assert True == (module1 is sys.modules['module1'])
    assert False == ('new_name' in sys.modules)
    assert True == (new_name is module1)
    assert True == (new_name is sys.modules['module1'])

s1 = set()
s2 = set()
s3 = set()

s1 = set(dir())
from module3 import *
s2 = set(dir())
from module4 import *
s3 = set(dir())

def test_module_star_import():
    # * imports are not allowed within functions, so we had to do it at global scope
    assert {'m3_func2', 'm3_func1'} == (s2 - s1)  # what did module3 import bring in.
    assert {'m4_func1', '_m4_func3'} == (s3 - s2)  # what did module4 import bring in.

three_things_i_learnt = """
-modules are imported and they should be present in present working directory
-modules are also with .py extendion only
-for knowing different functions and variables in a module use dir(module_name) and only a specific function can also be imported using from module_name import func_name
"""