The objective is to count the number of times each character appears in the sentence. To do that, we create a Python dictionary and update it as we pass through the sentence.
Step 1: Loop through every character in the sentence.
Step 2: Each time we encounter a character, we check if we have seen it before or if it’s the first time we’ve seen it. If we’ve already seen that character, we increment the counter by 1. That’s the line you asked about. If we have not seen it yet, we insert that letter into our dictionary and give it a value of 1. Every element in the Python dictionary contains a single letter as a key and a counter value equal to how many times we’ve seen that letter so far.
Step 3: Sort the Python dictionary so that the most frequently used letters are listed first. In this case, the most frequently used letter is a space ’ '. The second most used letter is ‘i’. The sorting routine could be updated to sort by the letter of the alphabet (the key) or the value. In this case, it sorts by value in descending order.
Step 4: Print out the list.
One note — on your last line, you printed only the first item in the Python dictionary. That happened to be a space. So the results of your script will only return a space and the number 6. There are six spaces because I also have a space as the first letter in the sentence. I removed that error and now it prints the entire list.
The correct output will look like this:
[(’ ', 6), (‘i’, 5), (‘s’, 3), (‘o’, 3), (‘n’, 3), (‘e’, 3), (‘m’, 2), (‘t’, 2), (‘T’, 1), (‘h’, 1), (‘a’, 1), (‘c’, 1), (‘r’, 1), (‘v’, 1), (‘w’, 1), (‘q’, 1), (‘u’, 1)]
Special note: I used github copilot as a coding assistant. I asked copilot to document the code. It wrote everything in the comments below. It’s a very handy tool and well worth the $10/month they charge. It writes code, debugs code, optimizes code, and explains code. I spent more time writing this post than I did documenting the code. 
# Import the pprint function from the pprint module
from pprint import pprint
# Initialize a string variable sentence with the value " This is a common interview question"
sentence = " This is a common interview question"
# Initialize an empty dictionary char_frequency
char_frequency = {}
# Start a for loop that iterates over each character char in the sentence
for char in sentence:
# Check if the character char is already a key in the char_frequency dictionary
if char in char_frequency:
# If it is, increment the value associated with that key by 1
char_frequency[char] += 1
else:
# If it's not, add the character as a new key to the dictionary with a value of 1
char_frequency[char] = 1
# Sort the char_frequency dictionary by value in descending order
char_frequency_sorted = sorted(
char_frequency.items(),
key = lambda kv: kv[1],
reverse=True)
# Print the sorted list of tuples to the console
print(char_frequency_sorted)
