How to detect method calls made by Python behind the scenes?

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In particular, I want to see which magic method is being called by a particular line of code.



For instance, I know that 1 + 2 actually calls (1).__add__(2) and [1,2,3][0] calls [1,2,3].__getitem__(0).



I'd like to know which magic methods are called for other operations without having to look it up online.




python




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  • 1




    use the dis module to get the opcode for the operation and then you can dig through ceval.c in the source code, which has a big switch on opcodes, to see where that takes you, but this can be non-trivial, depending on the operation
    – C S
    Aug 6 at 6:38














up vote
7
down vote

favorite
2












In particular, I want to see which magic method is being called by a particular line of code.



For instance, I know that 1 + 2 actually calls (1).__add__(2) and [1,2,3][0] calls [1,2,3].__getitem__(0).



I'd like to know which magic methods are called for other operations without having to look it up online.




python




share|improve this question

















  • 1




    use the dis module to get the opcode for the operation and then you can dig through ceval.c in the source code, which has a big switch on opcodes, to see where that takes you, but this can be non-trivial, depending on the operation
    – C S
    Aug 6 at 6:38












up vote
7
down vote

favorite
2









up vote
7
down vote

favorite
2






2





In particular, I want to see which magic method is being called by a particular line of code.



For instance, I know that 1 + 2 actually calls (1).__add__(2) and [1,2,3][0] calls [1,2,3].__getitem__(0).



I'd like to know which magic methods are called for other operations without having to look it up online.




python




share|improve this question













In particular, I want to see which magic method is being called by a particular line of code.



For instance, I know that 1 + 2 actually calls (1).__add__(2) and [1,2,3][0] calls [1,2,3].__getitem__(0).



I'd like to know which magic methods are called for other operations without having to look it up online.





python





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edited Aug 6 at 6:29









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asked Aug 6 at 6:23









japseow

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  • 1




    use the dis module to get the opcode for the operation and then you can dig through ceval.c in the source code, which has a big switch on opcodes, to see where that takes you, but this can be non-trivial, depending on the operation
    – C S
    Aug 6 at 6:38












  • 1




    use the dis module to get the opcode for the operation and then you can dig through ceval.c in the source code, which has a big switch on opcodes, to see where that takes you, but this can be non-trivial, depending on the operation
    – C S
    Aug 6 at 6:38







1




1




use the dis module to get the opcode for the operation and then you can dig through ceval.c in the source code, which has a big switch on opcodes, to see where that takes you, but this can be non-trivial, depending on the operation
– C S
Aug 6 at 6:38




use the dis module to get the opcode for the operation and then you can dig through ceval.c in the source code, which has a big switch on opcodes, to see where that takes you, but this can be non-trivial, depending on the operation
– C S
Aug 6 at 6:38










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There isn't a good way to inspect that. You should probably just look it up.



In the implementation (specifically for CPython), 1 + 2 or [1, 2, 3][0] won't actually go through the __add__ or __getitem__ methods at all; they'll go through C-level hooks and skip the methods entirely. Even if they went through the methods, it'd all happen in C-level code, which you can't debug with PDB or do much of anything to inspect.



The closest I have to something matching the spirit of what you're looking for is



>>> import unittest.mock
>>> unittest.mock.MagicMock() + 3
<MagicMock name='mock.__add__()' id='140290799397408'>


so hey, look! + uses __add__. That's something you can run to see what magic method is invoked for +. It doesn't involve actually inspecting the magic methods involved in +, though. MagicMock just has already-written implementations of most of the standard magic methods.






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    up vote
    8
    down vote













    There isn't a good way to inspect that. You should probably just look it up.



    In the implementation (specifically for CPython), 1 + 2 or [1, 2, 3][0] won't actually go through the __add__ or __getitem__ methods at all; they'll go through C-level hooks and skip the methods entirely. Even if they went through the methods, it'd all happen in C-level code, which you can't debug with PDB or do much of anything to inspect.



    The closest I have to something matching the spirit of what you're looking for is



    >>> import unittest.mock
    >>> unittest.mock.MagicMock() + 3
    <MagicMock name='mock.__add__()' id='140290799397408'>


    so hey, look! + uses __add__. That's something you can run to see what magic method is invoked for +. It doesn't involve actually inspecting the magic methods involved in +, though. MagicMock just has already-written implementations of most of the standard magic methods.






    share|improve this answer

























      up vote
      8
      down vote













      There isn't a good way to inspect that. You should probably just look it up.



      In the implementation (specifically for CPython), 1 + 2 or [1, 2, 3][0] won't actually go through the __add__ or __getitem__ methods at all; they'll go through C-level hooks and skip the methods entirely. Even if they went through the methods, it'd all happen in C-level code, which you can't debug with PDB or do much of anything to inspect.



      The closest I have to something matching the spirit of what you're looking for is



      >>> import unittest.mock
      >>> unittest.mock.MagicMock() + 3
      <MagicMock name='mock.__add__()' id='140290799397408'>


      so hey, look! + uses __add__. That's something you can run to see what magic method is invoked for +. It doesn't involve actually inspecting the magic methods involved in +, though. MagicMock just has already-written implementations of most of the standard magic methods.






      share|improve this answer























        up vote
        8
        down vote










        up vote
        8
        down vote









        There isn't a good way to inspect that. You should probably just look it up.



        In the implementation (specifically for CPython), 1 + 2 or [1, 2, 3][0] won't actually go through the __add__ or __getitem__ methods at all; they'll go through C-level hooks and skip the methods entirely. Even if they went through the methods, it'd all happen in C-level code, which you can't debug with PDB or do much of anything to inspect.



        The closest I have to something matching the spirit of what you're looking for is



        >>> import unittest.mock
        >>> unittest.mock.MagicMock() + 3
        <MagicMock name='mock.__add__()' id='140290799397408'>


        so hey, look! + uses __add__. That's something you can run to see what magic method is invoked for +. It doesn't involve actually inspecting the magic methods involved in +, though. MagicMock just has already-written implementations of most of the standard magic methods.






        share|improve this answer













        There isn't a good way to inspect that. You should probably just look it up.



        In the implementation (specifically for CPython), 1 + 2 or [1, 2, 3][0] won't actually go through the __add__ or __getitem__ methods at all; they'll go through C-level hooks and skip the methods entirely. Even if they went through the methods, it'd all happen in C-level code, which you can't debug with PDB or do much of anything to inspect.



        The closest I have to something matching the spirit of what you're looking for is



        >>> import unittest.mock
        >>> unittest.mock.MagicMock() + 3
        <MagicMock name='mock.__add__()' id='140290799397408'>


        so hey, look! + uses __add__. That's something you can run to see what magic method is invoked for +. It doesn't involve actually inspecting the magic methods involved in +, though. MagicMock just has already-written implementations of most of the standard magic methods.







        share|improve this answer













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        answered Aug 6 at 6:39









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