8 ms·

You can use pdb Just python -m pdb -m module

BiteCode_dev 3y ago
Damn, 15 years of python and I learn you can use -m twice. I've never even tried, didn't occur to me it would be supported. EDIT: it support other options as well, like -c. That deserves an alias: debug_module() { if python -c "import ipdb" &>/dev/null; then python -m ipdb -c c -m "$@" else python -m pdb -c c -m "$@" fi }
- abhishekjha 3y ago
  Like whats the general usage though? python -m http.server is the most I have done.
  - BiteCode_dev 3y ago
    -m pdb is post mortem debugging, it drops you in the debugger when it encounters the first unhandled exception. This is much easier than trying to pin point where to put a breakpoint.
- kzrdude 3y ago
  There's no magic, only layers. `python -m pdb <args>` runs pdb with the rest of the arguments. pdb handles the second `-m`. If you have a fancy IDE feature, open a new python file, type "import pdb", use go to definition on pdb to jump to that file in the standard library, and read its main function - it handles -m explicitly :)
  - sharikous 3y ago
    Speaking of pdb.. maybe someone knows why pdb has some issues with scope in its REPL that are resolved in VSCode's debugger and PyCharm? Multiline statements are not accepted, nor things like if/for Even list comprehensions and lambda expressions have trouble loading local variables defined via the REPL Are there workarounds? It would reduce the need for using IDEs. People who have experience with Julia and Matlab are very used to a trial and error programming style in a console and bare python does not address this need
    - BiteCode_dev 3y ago
      There are not workaround, pdb is a rustic tool. Since I still enjoy a cmdline debugger more than a graphical one, I use ipdb, which doesn't suffer from the multiline limitation. However, scoping issues with lambda and comprehension are actually a Python problem, not a pdb problem.
    - johnnymellor 3y ago
      Not supporting multi-line statements is just because pdb doesn't bother to parse the statement to work out if it is an incomplete multi-line statement. That could be easily fixed (I have a prototype patch for that using `code.compile_command`). The scope problems are more fundamental: The pdb REPL calls[1] the exec builtin as `exec(code, frame.f_globals, frame.f_locals)`, which https://docs.python.org/3/library/functions.html#exec https://docs.python.org/3/library/functions.html#exec documents as: "If exec gets two separate objects as globals and locals, the code will be executed as if it were embedded in a class definition." And https://docs.python.org/3/reference/executionmodel.html#resolution-of-names https://docs.python.org/3/reference/executionmodel.html#reso... documents that: "The scope of names defined in a class block is limited to the class block; it does not extend to the code blocks of methods - this includes comprehensions and generator expressions since they are implemented using a function scope." This is a fundamental limitation of `exec`. You can workaround it by only passing a single namespace dictionary to exec instead of passing separate globals and locals, which is what pdb's interact command does[2], but then it's ambiguous how to map changes to that dictionary back to the separate globals and locals dictionaries (pdb's interact command just discards any changes you make to the namespace). This too could be solved, but requires either brittle ast parsing or probably a PEP to add new functionality to exec. I'll file a bug against Python soon. [1]: https://github.com/python/cpython/blob/25a64fd28aaaaf2d21fae23212a0554c24fc7b20/Lib/pdb.py#L479 https://github.com/python/cpython/blob/25a64fd28aaaaf2d21fae... [2]: https://github.com/python/cpython/blob/25a64fd28aaaaf2d21fae23212a0554c24fc7b20/Lib/pdb.py#L1584 https://github.com/python/cpython/blob/25a64fd28aaaaf2d21fae...
      - johnnymellor 3y ago
        Oh, and multi-line statements will be supported from Python 3.13 (https://github.com/python/cpython/issues/103124 https://github.com/python/cpython/issues/103124)
- misnome 3y ago
  to be fair, it was only added in 3.7

Damn, 15 years of python and I learn you can use -m twice. I've never even tried, didn't occur to me it would be supported. EDIT: it support other options as well, like -c. That deserves an alias: debug_module() { if python -c "import ipdb" &>/dev/null; then python -m ipdb -c c -m "$@" else python -m pdb -c c -m "$@" fi }

abhishekjha 3y ago
Like whats the general usage though? python -m http.server is the most I have done.
- BiteCode_dev 3y ago
  -m pdb is post mortem debugging, it drops you in the debugger when it encounters the first unhandled exception. This is much easier than trying to pin point where to put a breakpoint.
kzrdude 3y ago
There's no magic, only layers. `python -m pdb <args>` runs pdb with the rest of the arguments. pdb handles the second `-m`. If you have a fancy IDE feature, open a new python file, type "import pdb", use go to definition on pdb to jump to that file in the standard library, and read its main function - it handles -m explicitly :)
- sharikous 3y ago
  Speaking of pdb.. maybe someone knows why pdb has some issues with scope in its REPL that are resolved in VSCode's debugger and PyCharm? Multiline statements are not accepted, nor things like if/for Even list comprehensions and lambda expressions have trouble loading local variables defined via the REPL Are there workarounds? It would reduce the need for using IDEs. People who have experience with Julia and Matlab are very used to a trial and error programming style in a console and bare python does not address this need
  - BiteCode_dev 3y ago
    There are not workaround, pdb is a rustic tool. Since I still enjoy a cmdline debugger more than a graphical one, I use ipdb, which doesn't suffer from the multiline limitation. However, scoping issues with lambda and comprehension are actually a Python problem, not a pdb problem.
  - johnnymellor 3y ago
    Not supporting multi-line statements is just because pdb doesn't bother to parse the statement to work out if it is an incomplete multi-line statement. That could be easily fixed (I have a prototype patch for that using `code.compile_command`). The scope problems are more fundamental: The pdb REPL calls[1] the exec builtin as `exec(code, frame.f_globals, frame.f_locals)`, which https://docs.python.org/3/library/functions.html#exec https://docs.python.org/3/library/functions.html#exec documents as: "If exec gets two separate objects as globals and locals, the code will be executed as if it were embedded in a class definition." And https://docs.python.org/3/reference/executionmodel.html#resolution-of-names https://docs.python.org/3/reference/executionmodel.html#reso... documents that: "The scope of names defined in a class block is limited to the class block; it does not extend to the code blocks of methods - this includes comprehensions and generator expressions since they are implemented using a function scope." This is a fundamental limitation of `exec`. You can workaround it by only passing a single namespace dictionary to exec instead of passing separate globals and locals, which is what pdb's interact command does[2], but then it's ambiguous how to map changes to that dictionary back to the separate globals and locals dictionaries (pdb's interact command just discards any changes you make to the namespace). This too could be solved, but requires either brittle ast parsing or probably a PEP to add new functionality to exec. I'll file a bug against Python soon. [1]: https://github.com/python/cpython/blob/25a64fd28aaaaf2d21fae23212a0554c24fc7b20/Lib/pdb.py#L479 https://github.com/python/cpython/blob/25a64fd28aaaaf2d21fae... [2]: https://github.com/python/cpython/blob/25a64fd28aaaaf2d21fae23212a0554c24fc7b20/Lib/pdb.py#L1584 https://github.com/python/cpython/blob/25a64fd28aaaaf2d21fae...
    - johnnymellor 3y ago
      Oh, and multi-line statements will be supported from Python 3.13 (https://github.com/python/cpython/issues/103124 https://github.com/python/cpython/issues/103124)
misnome 3y ago
to be fair, it was only added in 3.7