This code defines a function vowel_count that counts the number of vowels in a given string and then calls it with the string "Mathematics". Here's a breakdown of how it works:

Function Definition:

def vowel_count(str): defines a function named vowel_count that takes a single argument str, which is expected to be a string.
Counting Vowels:

vowels = 'aeiouAEIOU' creates a string variable vowels containing all lowercase and uppercase vowels.
count = len([char for char in str if char in vowels]) is the core part that counts the vowels. Let's break it down further:
[char for char in str if char in vowels] is a list comprehension. It iterates through each character (char) in the input string (str). If the character is present (in) the vowels string, it gets added to the list being built. This creates a list containing only the vowels from the input string.
len(...) then counts the number of elements in this list (which are the vowels) and assigns that count to the variable count.
Printing the Result:

print('No. of vowels:', count) prints a message "No. of vowels:" followed by the value stored in the count variable, which represents the number of vowels found.
Calling the Function:

str = 'Mathematics' assigns the string "Mathematics" to the variable str.
vowel_count(str) calls the vowel_count function, passing the string "Mathematics" as the argument. This executes the code inside the function with "Mathematics" being analyzed for vowels.
Overall, the code outputs the number of vowels in the string "Mathematics".

In this specific case, the output would be:

No. of vowels: 4