You can execute instructions in the bodies of loops like you can in functions. This means you can use everything you learned before inside loops, such as conditional constructions.
Imagine a function that counts how many times a letter occurs in a sentence. Example of how it works:
count_chars('Fear cuts deeper than swords.', 'e') # 4
# If nothing is found, the result is 0 matches
count_chars('Sansa', 'y') # 0
Before you look at the contents of a function, think about this:
def count_chars(string, char):
index = 0
count = 0
while index < len(string):
if string[index] == char:
# We only count the matching characters
count = count + 1
# The counter is incremented anyway
index = index + 1
return count
This is an aggregation task. Although it doesn't count all the characters to calculate the amount, you still have to analyze each character. The key difference between this loop and the ones we looked at before is that there's a condition inside the body.
The count
variable is incremented only when the character in question is the same as the expected one. Otherwise, it's a typical aggregate function that returns the number of characters you want.
The function from the theory is case-sensitive. I.e., A' and
a' are different characters from its point of view. Write a version of this function that isn't case-sensitive:
count_chars('HexlEt', 'e') # 2
count_chars('HexlEt', 'E') # 2
If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:
Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.
It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.
In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.
It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.
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Your exercise will be checked with these tests:
1import index
2
3
4def test1():
5 assert index.count_chars('axe', 'a') == 1
6 assert index.count_chars('', 'a') == 0
7 assert index.count_chars('opPa', 'p') == 2
8 assert index.count_chars('opPa', 'P') == 2
9
Teacher's solution will be available in: