Python: Cycle For

The while' loop can be used to solve any item search problem, but it is notable for being verbose. For while` it is necessary to set a stopping condition and enter a counter. When there are few loops, this is fine, but in real code loops occur at every step. It is therefore tedious to manage the conditions manually, especially when the stopping condition is obvious.

For example, if we want to go through the characters in a string, the computer can figure out by itself when the string ends. For such situations, Python introduced the for loop. It knows itself when to stop, because it only works with collections - sets of elements that need to be searched.

A string is a collection because it consists of a set of characters. The other types of collections are studied in detail in another course.

Example:

text = 'code'
for symbol in text:
    print(symbol)

# => c
# => o
# => d
# => e

In the code above, for goes through each character in the string, writes it in a variable symbol and calls the internal code block where that variable is used. The name of this variable can be anything. The general structure of the for' loop looks like this: for in '.

Let's see how to implement the string flip function through the for loop:

def reverse_string(text):
    # Initial value
    result = ''
    # char - a variable in which the current character is written
    for char in text:
        # Connect in reverse order
        result = char + result
    # The cycle ends when the whole line is passed
    return result


reverse_string('go!')  # => '!og'

Now let's calculate the number of mentions of a character in the string, not case-sensitive:

# text - any text
# char - a symbol to consider
def chars_count(text, char):
    # Since we are looking for the sum, the initial value is 0
    result = 0
    for current_char in text:
        # We convert everything to lower case,
        # so as not to depend on the current register
        if current_char.lower() == char.lower():
            result += 1
    return result


chars_count('hexlet!', 'e')  # 2
chars_count('hExlet!', 'e')  # 2
chars_count('hExlet!', 'E')  # 2

chars_count('hexlet!', 'a')  # 0

Instructions

In a previous lesson, we already wrote the filter_string() function. Recall that it takes a string and a character as input and returns a new string in which the passed character at all its positions is removed. This time, implement this function using the for loop. An additional condition: the case of the character to be eliminated does not matter.

An example of a call:

text = 'If I look forward I win'
filter_string(text, 'i')  # 'f  look forward  wn'
filter_string(text, 'O')  # 'If I lk frward I win'