Import Deep Dive

Presented at EuroPython 2015
https://ep2015.europython.eu/conference/talks/import-deep-dive

Transcript

1. Import Deep Dive
   Petr Viktorin
   @encukou
   encukou@gmail.com
   encukou.cz
   EuroPython 2015
   

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2. import random
   

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3. Prior art
   David Beazley — Modules and Packages: Live and Let Die!
   http://pyvideo.org/video/3387
   

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4. Photo © Paul Hermans, https://en.wikipedia.org/wiki/File:Tunnelaquarium_14-05-2009_15-54-09.JPG
   

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5. import random
   

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6. import random
   random = __import__('random')
   

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7. import random
   random = __import__('random')
   from ..spam import foo
   

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8. import random
   random = __import__('random')
   from ..spam import foo
   foo = __import__('spam', globals(), locals(), ['foo'], 2).foo
   https://docs.python.org/3/library/functions.html#__import__
   

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9. import random
   random = __import__('random')
   

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10. import random
    random = __import__('random')
    The Import Machinery
    

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11. import random
    random = __import__('random')
    The Import Machinery
    importlib.import_module('random')
    

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12. import random
    The Import Machinery
    importlib.import_module('random')
    

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13. The Import Machinery
    Photo © Les Chatfield, https://www.flickr.com/photos/elsie/8229790
    

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14. The Import Machinery
    Photo © Les Chatfield, https://www.flickr.com/photos/elsie/8229790
    sans:
    • Locking
    • Caching
    • Error handling
    • Pythons older than 3.4
    • Backwards compatibility shims
    

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15. importlib.import_module('random')
    

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16. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    >>> import random
    >>> old = random
    >>> import random
    >>> random is old
    True
    

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17. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    >>> import random
    >>> old = random
    >>> import random
    >>> random is old
    True
    

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18. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    >>> import random
    >>> old = random
    >>> import random
    >>> random is old
    True
    

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19. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    >>> import random
    >>> old = random
    >>> del sys.modules['random']
    >>> import random
    >>> random is old
    False
    >>> (random.sample is
    ... old.sample)
    False
    >>> sys.modules['impostor'] = 'Not a module, is it?'
    >>> import impostor
    >>> impostor[:12]
    'Not a module'
    

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20. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    >>> import random
    >>> old = random
    >>> del sys.modules['random']
    >>> import random
    >>> random is old
    False
    >>> (random.sample is
    ... old.sample)
    False
    >>> sys.modules['impostor'] = 'Not a module, is it?'
    >>> import impostor
    >>> impostor[:12]
    'Not a module'
    

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21. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    >>> sys.path
    ['',
    '/usr/lib64/python34.zip',
    '/usr/lib64/python3.4',
    ...]
    >>> importlib.util.find_spec('antigravity')
    ModuleSpec(name='antigravity',
    loader=<_frozen_importlib.SourceFileLoader ...>,
    origin='/usr/lib64/python3.4/antigravity.py')
    >>> import io
    >>> io.__spec__
    ModuleSpec(name='io',
    loader=<_frozen_importlib.SourceFileLoader ...>,
    origin='/usr/lib64/python3.4/io.py')
    

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22. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    >>> sys.path
    ['',
    '/usr/lib64/python34.zip',
    '/usr/lib64/python3.4',
    ...]
    >>> importlib.util.find_spec('antigravity')
    ModuleSpec(name='antigravity',
    loader=<_frozen_importlib.SourceFileLoader ...>,
    origin='/usr/lib64/python3.4/antigravity.py')
    >>> import io
    >>> io.__spec__
    ModuleSpec(name='io',
    loader=<_frozen_importlib.SourceFileLoader ...>,
    origin='/usr/lib64/python3.4/io.py')
    

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23. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    >>> sys.path
    ['',
    '/usr/lib64/python34.zip',
    '/usr/lib64/python3.4',
    ...]
    >>> importlib.util.find_spec('antigravity')
    ModuleSpec(name='antigravity',
    loader=<_frozen_importlib.SourceFileLoader ...>,
    origin='/usr/lib64/python3.4/antigravity.py')
    >>> import io
    >>> io.__spec__
    ModuleSpec(name='io',
    loader=<_frozen_importlib.SourceFileLoader ...>,
    origin='/usr/lib64/python3.4/io.py')
    

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24. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    >>> sys.path
    ['',
    '/usr/lib64/python34.zip',
    '/usr/lib64/python3.4',
    ...]
    >>> importlib.util.find_spec('antigravity')
    ModuleSpec(name='antigravity',
    loader=<_frozen_importlib.SourceFileLoader ...>,
    origin='/usr/lib64/python3.4/antigravity.py')
    >>> import io
    >>> io.__spec__
    ModuleSpec(name='io',
    loader=<_frozen_importlib.SourceFileLoader ...>,
    origin='/usr/lib64/python3.4/io.py')
    

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25. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    • Put module in sys.modules
    • Initialize the module
    

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26. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    foo.py:
    import bar
    bar.do_bar()
    def do_foo():
    print('Fooing!')
    bar.py:
    import foo
    foo.do_foo()
    def do_bar():
    print('Barring!')
    • Put module in sys.modules
    • Initialize the module
    

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27. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    foo.py:
    import bar
    bar.do_bar()
    def do_foo():
    print('Fooing!')
    bar.py:
    import foo
    foo.do_foo()
    def do_bar():
    print('Barring!')
    • Put module in sys.modules
    • Initialize the module
    

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28. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    foo.py:
    import bar
    bar.do_bar()
    def do_foo():
    print('Fooing!')
    bar.py:
    import foo
    foo.do_foo()
    def do_bar():
    print('Barring!')
    • Put module in sys.modules
    • Initialize the module
    

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29. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    foo.py:
    import bar
    bar.do_bar()
    def do_foo():
    print('Fooing!')
    bar.py:
    import foo
    foo.do_foo()
    def do_bar():
    print('Barring!')
    • Put module in sys.modules
    • Initialize the module
    

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30. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    foo.py:
    import bar
    bar.do_bar()
    def do_foo():
    print('Fooing!')
    bar.py:
    import foo
    foo.do_foo()
    def do_bar():
    print('Barring!')
    • Put module in sys.modules
    • Initialize the module
    

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31. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    

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32. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    Filename Module name
    random.py random
    urllib/
    __init__.py urllib
    parse.py urllib.parse
    request.py urllib.request
    response.py urllib.response
    Top-level module
    Package
    Parent of the below
    Submodule
    

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33. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    Filename Module name
    random.py random
    urllib/
    __init__.py urllib
    parse.py urllib.parse
    request.py urllib.request
    response.py urllib.response
    Top-level module
    Package
    Parent of the below
    Submodule
    

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34. import_module(name):
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    return module
    import urllib.parse
    >>> urllib.__path__
    ['/usr/lib64/python3.4/urllib']
    Filename Module name
    random.py random
    urllib/
    __init__.py urllib
    parse.py urllib.parse
    request.py urllib.request
    response.py urllib.response
    Top-level module
    Package
    Parent of the below
    Submodule
    

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35. import_module(name):
    sys.modules[name]? return it
    submodules:
    load parent module
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    submodules:
    set module as attribute of parent
    return module
    import urllib.parse
    >>> urllib.__path__
    ['/usr/lib64/python3.4/urllib']
    Filename Module name
    random.py random
    urllib/
    __init__.py urllib
    parse.py urllib.parse
    request.py urllib.request
    response.py urllib.response
    Top-level module
    Package
    Parent of the below
    Submodule
    

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36. import_module(name):
    sys.modules[name]? return it
    submodules:
    load parent module
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    submodules:
    set module as attribute of parent
    return module
    • Put module in sys.modules
    • Initialize the module
    

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37. import_module(name):
    sys.modules[name]? return it
    submodules:
    load parent module
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    submodules:
    set module as attribute of parent
    return module
    foo/__init__.py:
    from foo import main
    from foo import consts
    foo/main.py:
    import foo
    use(foo.consts.value)
    foo/consts.py:
    value = 42
    • Put module in sys.modules
    • Initialize the module
    

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38. import_module(name):
    sys.modules[name]? return it
    submodules:
    load parent module
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    submodules:
    set module as attribute of parent
    return module
    foo/__init__.py:
    from foo import main
    from foo import consts
    foo/main.py:
    import foo
    use(foo.consts.value)
    foo/consts.py:
    value = 42
    • Put module in sys.modules
    • Initialize the module
    

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39. import_module(name):
    sys.modules[name]? return it
    submodules:
    load parent module
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    submodules:
    set module as attribute of parent
    return module
    foo/__init__.py:
    from foo import main
    from foo import consts
    foo/main.py:
    import foo
    use(foo.consts.value)
    foo/consts.py:
    value = 42
    • Put module in sys.modules
    • Initialize the module
    

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40. import_module(name):
    sys.modules[name]? return it
    submodules:
    load parent module
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    submodules:
    set module as attribute of parent
    return module
    foo/__init__.py:
    from foo import main
    from foo import consts
    foo/main.py:
    import foo
    use(foo.consts.value)
    foo/consts.py:
    value = 42
    • Put module in sys.modules
    • Initialize the module
    

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41. import_module(name):
    sys.modules[name]? return it
    submodules:
    load parent module
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    submodules:
    set module as attribute of parent
    return module
    foo/__init__.py:
    from foo import main
    from foo import consts
    foo/main.py:
    import foo
    use(foo.consts.value)
    foo/consts.py:
    value = 42
    • Put module in sys.modules
    • Initialize the module
    

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42. import_module(name):
    sys.modules[name]? return it
    submodules:
    load parent module
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    submodules:
    set module as attribute of parent
    return module
    foo/__init__.py:
    from foo import main
    from foo import consts
    foo/main.py:
    import foo
    use(foo.consts.value)
    foo/consts.py:
    value = 42
    • Put module in sys.modules
    • Initialize the module
    

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43. import_module(name):
    sys.modules[name]? return it
    submodules:
    load parent module
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    submodules:
    set module as attribute of parent
    return module
    foo/__init__.py:
    from foo import main
    from foo import consts
    foo/main.py:
    import foo
    use(foo.consts.value)
    foo/consts.py:
    value = 42
    • Put module in sys.modules
    • Initialize the module
    

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44. __init__ should:
    import from submodules
    set __all__
    nothing else
    submodules should:
    not import directly from __init__
    not have internal import cycles
    

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45. import_module(name):
    sys.modules[name]? return it
    submodules:
    load parent module
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    submodules:
    set module as attribute of parent
    return module
    ?
    

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46. Where's the module?
    >>> import random
    >>> random
    
    >>> random.__file__
    '/usr/lib64/python3.4/random.py'
    >>> import sys
    >>> sys
    
    >>> sys.__file__
    Traceback (most recent call last):
    File "", line 1, in
    AttributeError: 'module' object has no attribute '__file__'
    /usr/bin/python3
    

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47. Where's the module?
    >>> import random
    >>> random
    
    >>> random.__file__
    '/usr/lib64/python3.4/random.py'
    >>> import sys
    >>> sys
    
    >>> sys.__file__
    Traceback (most recent call last):
    File "", line 1, in
    AttributeError: 'module' object has no attribute '__file__'
    /usr/bin/python3
    

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48. Where's the module?
    >>> import random
    >>> random
    
    >>> random.__file__
    '/usr/lib64/python3.4/random.py'
    >>> import sys
    >>> sys
    
    >>> sys.__file__
    Traceback (most recent call last):
    File "", line 1, in
    AttributeError: 'module' object has no attribute '__file__'
    /usr/bin/python3
    

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49. Where's the module?
    >>> import random
    >>> random
    
    >>> random.__file__
    '/usr/lib64/python3.4/random.py'
    >>> import sys
    >>> sys
    
    >>> sys.__file__
    Traceback (most recent call last):
    File "", line 1, in
    AttributeError: 'module' object has no attribute '__file__'
    /usr/bin/python3
    

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50. Where's the module?
    >>> import random
    >>> random
    
    >>> random.__file__
    '/usr/lib64/python3.4/random.py'
    >>> import sys
    >>> sys
    
    >>> sys.__file__
    Traceback (most recent call last):
    File "", line 1, in
    AttributeError: 'module' object has no attribute '__file__'
    /usr/bin/python3
    

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51. Where's the module?
    >>> import random
    >>> random
    
    >>> random.__file__
    '/usr/lib64/python3.4/random.py'
    >>> import sys
    >>> sys
    
    >>> sys.__file__
    Traceback (most recent call last):
    File "", line 1, in
    AttributeError: 'module' object has no attribute '__file__'
    /usr/bin/python3
    

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52. Where's the module?
    >>> import random
    >>> random
    
    >>> random.__file__
    '/usr/lib64/python3.4/random.py'
    >>> import sys
    >>> sys
    
    >>> sys.__file__
    Traceback (most recent call last):
    File "", line 1, in
    AttributeError: 'module' object has no attribute '__file__'
    /usr/bin/python3
    

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53. Photo © Allentchang, https://commons.wikimedia.org/wiki/File:Fish_in_Okinawa_Churaumi_Aquarium.JPG
    C Python
    Compiled in Built-in Frozen
    From File Extension Source
    sys _frozen_importlib
    math random
    

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54. Photo © Allentchang, https://commons.wikimedia.org/wiki/File:Fish_in_Okinawa_Churaumi_Aquarium.JPG
    C Python
    Compiled in Built-in Frozen
    From File Extension Source
    sys _frozen_importlib
    math random
    

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55. Photo © Allentchang, https://commons.wikimedia.org/wiki/File:Fish_in_Okinawa_Churaumi_Aquarium.JPG
    C Python
    Compiled in Built-in Frozen
    From File Extension Source
    sys _frozen_importlib
    math random
    

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56. >>> sys.meta_path
    [,
    ,
    ]
    

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57. find_spec(name, path):
    for finder in sys.meta_path:
    call its find_spec(name, path)
    return spec if successful
    >>> sys.meta_path
    [,
    ,
    ]
    

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58. find_spec(name, path):
    for finder in sys.meta_path:
    call its find_spec(name, path)
    return spec if successful
    >>> sys.meta_path
    [,
    ,
    ]
    >>> sys.path
    ['', '/usr/lib64/python34.zip', '/usr/lib/python3.4', ...]
    

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59. find_spec(name, path):
    for finder in sys.meta_path:
    call its find_spec(name, path)
    return spec if successful
    >>> sys.meta_path
    [,
    ,
    ]
    >>> sys.path_hooks
    [,
    ]
    >>> sys.path
    ['', '/usr/lib64/python34.zip', '/usr/lib/python3.4', ...]
    

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60. find_spec(name, path):
    for finder in sys.meta_path:
    call its find_spec(name, path)
    return spec if successful
    PathFinder.find_spec(name, path):
    for directory in path:
    get sys.path_hooks entry
    call its find_spec(name)
    return spec if successful
    >>> sys.meta_path
    [,
    ,
    ]
    >>> sys.path_hooks
    [,
    ]
    >>> sys.path
    ['', '/usr/lib64/python34.zip', '/usr/lib/python3.4', ...]
    

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61. find_spec(name, path):
    for finder in sys.meta_path:
    call its find_spec(name, path)
    return spec if successful
    PathFinder.find_spec(name, path):
    for directory in path:
    get sys.path_hooks entry
    call its find_spec(name)
    return spec if successful
    >>> sys.meta_path
    [,
    ,
    ]
    >>> sys.path_hooks
    [,
    ]
    >>> sys.path
    ['', '/usr/lib64/python34.zip', '/usr/lib/python3.4', ...]
    random.cpython-34m.so (Extension module)
    random.abi3.so (Extension module)
    random.so (Extension module)
    random.py (Source module)
    random.pyc (Sourceless module)
    

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62. find_spec(name, path):
    for finder in sys.meta_path:
    call its find_spec(name, path)
    return spec if successful
    PathFinder.find_spec(name, path):
    for directory in path:
    get sys.path_hooks entry
    call its find_spec(name)
    return spec if successful
    ModuleSpec:
    name
    random
    origin
    /usr/lib64/python3.4/random.py
    cached
    /usr/lib64/python3.4/__pycache__/random.cpython-34.pyc
    loader
    importlib.machinery.SourceFileLoader
    loader_state, parent, submodule_search_locations
    

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63. import_module(name):
    sys.modules[name]? return it
    submodules:
    load parent module
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    submodules:
    set module as attribute of parent
    return module
    ?
    

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64. load(spec):
    module = spec.loader.create_module(spec)
    if module is None:
    module = types.ModuleType(spec.name)
    set initial module attributes
    sys.modules[spec.name] = module
    spec.loader.exec_module(module, spec)
    

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65. load(spec):
    module = spec.loader.create_module(spec)
    if module is None:
    module = types.ModuleType(spec.name)
    set initial module attributes
    sys.modules[spec.name] = module
    spec.loader.exec_module(module, spec)
    

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66. load(spec):
    module = spec.loader.create_module(spec)
    if module is None:
    module = types.ModuleType(spec.name)
    set initial module attributes
    sys.modules[spec.name] = module
    spec.loader.exec_module(module, spec)
    spec → __spec__
    spec.name → __name__
    spec.loader → __loader__
    spec.parent → __package__
    spec.origin → __file__
    spec.cached → __cached__
    spec.submodule_search_locations
    → __path__
    

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67. load(spec):
    module = spec.loader.create_module(spec)
    if module is None:
    module = types.ModuleType(spec.name)
    set initial module attributes
    sys.modules[spec.name] = module
    spec.loader.exec_module(module, spec)
    spec → __spec__
    spec.name → __name__
    spec.loader → __loader__
    spec.parent → __package__
    spec.origin → __file__
    spec.cached → __cached__
    spec.submodule_search_locations
    → __path__
    >>> import __main__
    >>> a = 'hello'
    >>> __main__.a
    'hello'
    >>> __main__.a = 'world'
    >>> a
    'world'
    

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68. load(spec):
    module = spec.loader.create_module(spec)
    if module is None:
    module = types.ModuleType(spec.name)
    set initial module attributes
    sys.modules[spec.name] = module
    spec.loader.exec_module(module, spec)
    spec → __spec__
    spec.name → __name__
    spec.loader → __loader__
    spec.parent → __package__
    spec.origin → __file__
    spec.cached → __cached__
    spec.submodule_search_locations
    → __path__
    >>> import __main__
    >>> a = 'hello'
    >>> __main__.a
    'hello'
    >>> __main__.a = 'world'
    >>> a
    'world'
    if __name__ == '__main__'
    

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69. load(spec):
    module = spec.loader.create_module(spec)
    if module is None:
    module = types.ModuleType(spec.name)
    set initial module attributes
    sys.modules[spec.name] = module
    spec.loader.exec_module(module, spec)
    spec → __spec__
    spec.name → __name__
    spec.loader → __loader__
    spec.parent → __package__
    spec.origin → __file__
    spec.cached → __cached__
    spec.submodule_search_locations
    → __path__
    >>> import __main__
    >>> a = 'hello'
    >>> __main__.a
    'hello'
    >>> __main__.a = 'world'
    >>> a
    'world'
    if __name__ == '__main__'
    

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70. load(spec):
    module = spec.loader.create_module(spec)
    if module is None:
    module = types.ModuleType(spec.name)
    set initial module attributes
    sys.modules[spec.name] = module
    spec.loader.exec_module(module, spec)
    • Put module in sys.modules
    • Initialize the module
    

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71. get_code(module, spec):
    if spec.cached exists, and matches origin stats,
    return it!
    load source from origin and compile it
    write bytecode to spec.cached
    ModuleSpec:
    name
    random
    origin
    /usr/lib64/python3.4/random.py
    cached
    /usr/lib64/python3.4/__pycache__/random.cpython-34.pyc
    ...
    

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72. get_code(module, spec):
    if spec.cached exists, and matches origin stats,
    return it!
    load source from origin and compile it
    write bytecode to spec.cached
    Python 2
    somemodule.py
    somemodule.pyc
    

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73. get_code(module, spec):
    if spec.cached exists, and matches origin stats,
    return it!
    load source from origin and compile it
    write bytecode to spec.cached
    Python 2
    somemodule.py
    somemodule.pyc
    

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74. get_code(module, spec):
    if spec.cached exists, and matches origin stats,
    return it!
    load source from origin and compile it
    write bytecode to spec.cached
    Python 2
    somemodule.py
    somemodule.pyc
    Python 3
    somemodule.py
    __pycache__/
    somemodule.cpython-34.pyc
    

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75. get_code(module, spec):
    if spec.cached exists, and matches origin stats,
    return it!
    load source from origin and compile it
    write bytecode to spec.cached
    Python 2
    somemodule.py
    somemodule.pyc
    Python 3
    somemodule.py
    __pycache__/
    somemodule.cpython-34.pyc
    Or:
    somemodule.py
    somemodule.pyc
    

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76. import_module(name):
    sys.modules[name]? return it
    submodules:
    load parent module
    sys.modules[name]? return it
    spec = find_spec(name, path)
    load(spec)
    module = sys.modules[name]
    submodules:
    set module as attribute of parent
    return module
    find_spec(name, path):
    for finder in sys.meta_path:
    call its find_spec(name, path)
    return spec if successful
    PathFinder.find_spec(name, path):
    for directory in path:
    get sys.path_hooks entry
    call its find_spec(name)
    return spec if successful
    load(spec):
    module = spec.loader.create_module(spec)
    if module is None:
    module = types.ModuleType(spec.name)
    set initial module attributes
    sys.modules[spec.name] = module
    spec.loader.exec_module(module, spec)
    get_code(module, spec):
    if spec.cached exists, and matches origin stats,
    return it!
    load source from origin and compile it
    write bytecode to spec.cached
    

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77. C Python Bytecode
    Compiled-in Built-in Frozen
    From File Extension Sourceless
    Zip file zip source zip sourceless
    Source
    

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