UserWarning: converting a masked element to nan

Executing a python script (way to long to include here) I wrote leads to a warning message. I don’t know at which line in my code this gets raised. How can I get this information?

Furthermore, what does this mean exactly? In fact, I didn’t know I was using a masked array of some sort?

/usr/lib/pymodules/python2.7/numpy/ma/core.py:3785: UserWarning: Warning: converting a masked element to nan.
warnings.warn("Warning: converting a masked element to nan.")

Answer

You can use the warnings module to convert warnings to exceptions. The simplest method is called simplefilter. Here’s an example; the code that generates the warning is in func2b(), so there is a nontrival traceback.

import warnings


def func1():
    print("func1")

def func2():
    func2b()
    print("func2")

def func2b():
    warnings.warn("uh oh")

def func3():
    print("func3")


if __name__ == "__main__":
    # Comment the following line to see the default behavior.
    warnings.simplefilter('error', UserWarning)
    func1()
    func2()
    func3()

When the line containing the call to simplefilter is commented out, the output is

func1
warning_to_exception.py:13: UserWarning: uh oh
  warnings.warn("uh oh")
func2
func3

With that line included, you get a traceback:

func1
Traceback (most recent call last):
  File "warning_to_exception.py", line 23, in <module>
    func2()
  File "warning_to_exception.py", line 9, in func2
    func2b()
  File "warning_to_exception.py", line 13, in func2b
    warnings.warn("uh oh")
UserWarning: uh oh