AssertionLib

A package for performing assertions and providing informative exception messages.

Installation

• PyPi: pip install AssertionLib

• GitHub: pip install git+https://github.com/nlesc-nano/AssertionLib

Usage

A comprehensive overview of all available assertion methods is provided in the documentation. A few examples of some basic assertion:

>>> import numpy as np
>>> from assertionlib import assertion

# Assert the output of specific callables
>>> assertion.eq(5, 5)  # 5 == 5
>>> assertion.lt(5, 6)  # 5 < 6
>>> assertion.gt(6, 5)  # 5 > 6
>>> assertion.isinstance(5, int)
>>> assertion.hasattr(5, '__init__')
>>> assertion.any([False, False, True])
>>> assertion.isfinite(1.0)

# Simply assert a value
>>> assertion(5 == 5)
>>> assertion(isinstance(5, int))

# Apply post-processing before conducting the assertion
>>> ar_large = np.ones(10)
>>> ar_small = np.zeros(10)
>>> assertion.gt(ar_large, ar_small, post_process=np.all)  # all(ar_large > ar_small)

# Perform an assertion which will raise an AssertionError
>>> assertion.eq(5, 6, message='Fancy custom error message')  # 5 == 6
Traceback (most recent call last):
  ...
AssertionError: output = eq(a, b); assert output

exception: AssertionError = AssertionError('Fancy custom error message')

output: bool = False
a: int = 5
b: int = 6

A few examples of AssertionErrors raised due to incorrect method signatures:

>>> from assertionlib import assertion

>>> assertion.len(5)
Traceback (most recent call last):
  ...
AssertionError: output = len(obj); assert output

exception: TypeError = TypeError("object of type 'int' has no len()")

output: NoneType = None
obj: int = 5

>>> from assertionlib import assertion

>>> assertion.eq(5, 5, 5, 5)
Traceback (most recent call last):
  ...
AssertionError: output = eq(a, b, _a, _b); assert output

exception: TypeError = TypeError('eq expected 2 arguments, got 4')

output: NoneType = None
a: int = 5
b: int = 5
_a: int = 5
_b: int = 5

A demonstration of the exception parameter. Providing an exception type will assert that the provided exception is raised during/before the assertion process:

>>> from assertionlib import assertion

>>> len(5)
Traceback (most recent call last):
  ...
TypeError: object of type 'int' has no len()

>>> from assertionlib import assertion

>>> assertion.len(5, exception=TypeError)  # i.e. len(5) should raise a TypeError
>>> assertion.len([5], exception=TypeError)
Traceback (most recent call last):
  ...
AssertionError: output = len(obj); assert output

exception: AssertionError = AssertionError("Failed to raise 'TypeError'")

output: int = 1
obj: list = [5]

Lastly, the output of custom callables can be asserted in one of the following two ways, supplying the callable to AssertionManager.assert() or creating a custom assertion method and adding it to an instance with AssertionManager.add_to_instance():

>>> from assertionlib import assertion

>>> def my_fancy_func(a: object) -> bool:
...     return False

# Approach #1, supply to-be asserted callable to assertion.assert_()
>>> assertion.assert_(my_fancy_func, 5)
Traceback (most recent call last):
  ...
AssertionError: output = my_fancy_func(a); assert output

exception: AssertionError = AssertionError(None)

output: bool = False
a: int = 5

>>> from assertionlib import assertion

# Approach #2, permanantly add a new bound method using assertion.add_to_instance()
>>> assertion.add_to_instance(my_fancy_func)
>>> assertion.my_fancy_func(5)
Traceback (most recent call last):
  ...
AssertionError: output = my_fancy_func(a); assert output

exception: AssertionError = AssertionError(None)

output: bool = False
a: int = 5