Assert
Contents
Assert#
Programming for Geoscientists Data Science and Machine Learning for Geoscientists
Assert statement allows us to do sanity checks in our code. It is also a very handy tool in preventing bugs that do not throw an Error
. Consider the following factorial function:
def fact(n):
result = 1
for i in range(n):
result*=i
return result
fact(-1)
1
What if \(n = 1.5\), \(n = -1\) or \(n \) is not a numeric type? Our function is defined for non-negative integers only. However, for some of those invalid inputs, the function can actually return something! assert
is a great feature to add here:
def fact(n):
assert n is int and n >=0
result = 1
for i in range(n):
result*=i
return result
fact(-1)
---------------------------------------------------------------------------
AssertionError Traceback (most recent call last)
<ipython-input-9-0ca68cd43ada> in <module>
5 result*=i
6 return result
----> 7 fact(-1)
<ipython-input-9-0ca68cd43ada> in fact(n)
1 def fact(n):
----> 2 assert n is int and n >=0
3 result = 1
4 for i in range(n):
5 result*=i
AssertionError:
Now our program throws an AssertionError
and we immediately know that the input is invalid. While in this simple example such precautions might seem to be an overkill, assert
scales very well. When multiple functions exchange data, this feature might shorten the debugging time a lot.
If you do not want your program to crash because of the AssertionError
surround your code with the try..except
block:
def fact(n):
try:
assert n is int and n >=0
result = 1
for i in range(n):
result*=i
return result
except AssertionError:
print("This is an invalid input")
fact(-1)
This is an invalid input
In some coding regimes, assert
is considered acceptable only in the development process. It is often deactivated
in the final version of the software.
Exercises#
Perimeter of a circle Define a function which calculates the perimeter of a circle given its radius.
HINT: import math
for the value of \(\pi\). Do not assume that r
is of any particular type.
Answer
from math import pi
def perimeter(r):
assert r >=0
return 2* math.pi*r