PyCall error, number of arguments in a ccall function

General Usage
1

I have a script that calls functions from the Python OpenCV module via PyCall. Everything was working fine the other day, not sure what changed in my configuration. I use PyCall with my system python at /usr/bin/python3. Just tried to re-build PyCall already. What could cause this?

ERROR: PyError ($(Expr(:escape, :(ccall(#= /home/user/.julia/packages/PyCall/3fwVL/src/pyfncall.jl:43 =# @pysym(:PyObject_Call), PyPtr, (PyPtr, PyPtr, PyPtr), o, pyargsptr, kw))))) <class 'TypeError'>
TypeError('function takes exactly 2 arguments (3 given)')

Stacktrace:
  [1] pyerr_check
    @ ~/.julia/packages/PyCall/3fwVL/src/exception.jl:62 [inlined]
  [2] pyerr_check
    @ ~/.julia/packages/PyCall/3fwVL/src/exception.jl:66 [inlined]
  [3] _handle_error(msg::String)
    @ PyCall ~/.julia/packages/PyCall/3fwVL/src/exception.jl:83
  [4] macro expansion
    @ ~/.julia/packages/PyCall/3fwVL/src/exception.jl:97 [inlined]
  [5] #107
    @ ~/.julia/packages/PyCall/3fwVL/src/pyfncall.jl:43 [inlined]
  [6] disable_sigint
    @ ./c.jl:458 [inlined]
  [7] __pycall!
    @ ~/.julia/packages/PyCall/3fwVL/src/pyfncall.jl:42 [inlined]
  [8] _pycall!(ret::PyObject, o::PyObject, args::Tuple{PyObject, PyObject, PyObject, PyObject, Tuple{Int64, Int64, Int64}, PyObject, PyObject}, nargs::Int64, kw::Ptr{Nothing})
    @ PyCall ~/.julia/packages/PyCall/3fwVL/src/pyfncall.jl:29
  [9] _pycall!(ret::PyObject, o::PyObject, args::Tuple{PyObject, PyObject, PyObject, PyObject, Tuple{Int64, Int64, Int64}, PyObject, PyObject}, kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
    @ PyCall ~/.julia/packages/PyCall/3fwVL/src/pyfncall.jl:11
 [10] (::PyObject)(::PyObject, ::Vararg{Any}; kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
    @ PyCall ~/.julia/packages/PyCall/3fwVL/src/pyfncall.jl:86
 [11] (::PyObject)(::PyObject, ::Vararg{Any})
    @ PyCall ~/.julia/packages/PyCall/3fwVL/src/pyfncall.jl:86
 [12] top-level scope
2

That’s an ordinary Python TypeError saying a function was called with the wrong number of arguments. You should be able to use standard Python debugging tools like pdb to figure out where the problem is.

2 Likes
3

Thanks for the reassurance. :slight_smile: Damn, that was cryptic. The problem is that one argument I was passing to a function with 7 parameters was a tuple that is supposed to have 2 elements, and I had 3 elements there! So it’s probably some implicit intermediary function call that was failing.