

In [ ]:

    
import warnings
import numpy.testing as npt
import numpy as np
import sys

Resources

Errors & Exceptions in Python: https://docs.python.org/3/tutorial/errors.html
Built-In Excpetions in Python: https://docs.python.org/2/library/exceptions.html
Numpy Testing: http://docs.scipy.org/doc/numpy/reference/routines.testing.html

Assert statements

Example: Assert that a specific version of Python is being used



In [ ]:

    
def check_python_version():
    print 'Python version:\n', sys.version
    assert sys.version_info < (3,0)



In [ ]:

    
check_python_version()



In [ ]:

    
def improved_check_python_version():
    print 'Python version:\n', sys.version
    try:
        assert sys.version_info < (3,0)
    except:        
        raise AssertionError('Incompatible version of Python: use Python version < 3.0')



In [ ]:

    
improved_check_python_version()

Raising errors

Anticipate and catch errors
Raise a more informative error than the default error

Example: Division in Python versions < 3.0



In [ ]:

    
def test_type_float(var):
    if not isinstance(var, float):
        raise TypeError('Expected input type == float')



In [ ]:

    
f = 1.



In [ ]:

    
# Since the input type is a float, no error is raised.
test_type_float(f)



In [ ]:

    
i = 1



In [ ]:

    
# Since the input type is a list, an error is raised.
test_type_float(i)



In [ ]:

    
def incorrect_divide_by_two(var):
    return var / 2



In [ ]:

    
print incorrect_divide_by_two(f)



In [ ]:

    
print incorrect_divide_by_two(i)



In [ ]:

    
def correct_divide_by_two(var):
    '''
    Divides input by two.
    
    INPUT
    var : float
    '''
    test_type_float(var)
    return var / 2



In [ ]:

    
correct_divide_by_two?



In [ ]:

    
print correct_divide_by_two(f)



In [ ]:

    
print correct_divide_by_two(i)

Raising warnings

Example: Division in Python versions < 3.0



In [ ]:

    
def divide_by_two(var):
    if isinstance(var, int):
        warnings.warn('Performing floor division. Input type == int', Warning)
    return var / 2



In [ ]:

    
divide_by_two(1)



In [ ]:

    
divide_by_two(np.array([1]))



In [ ]:

    
def divide_by_two(var):
    if isinstance(var, int):
        warnings.warn('Performing floor division. Input type == int', Warning)
    if isinstance(var, np.ndarray):
        if var.dtype == int:
            warnings.warn('Performing floor division. numpy.dtype == int', Warning)
    return var / 2



In [ ]:

    
divide_by_two(np.array([1]))



In [ ]: