Strings

'this is a string'

'this is a string'

🎨 len

len('word and word')

13

You can use len to get the length of a string.

🖌 Building Strings

'fire' + 'place'

'fireplace'

'yo' * 2

'yoyo'

'nan ' * 16 + 'batman!'

'nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan batman!'

🖌 +=

message = 'Hello'
message = message + ' world!'
message

'Hello world!'

message = 'Hello'
message += ' world!'
message

'Hello world!'

🖌 String Iteration

for letter in 'this is a string':
    print(letter)

t
h
i
s
 
i
s
 
a
 
s
t
r
i
n
g

🎨 Character classes

'a'.isalpha(), '8'.isalpha()

(True, False)

'!' < '0'

True

'abcdefg'.isalpha(), 'abc1234'.isalpha(), 'abc!'.isalpha()

(True, False, False)

'a'.isdigit(), '8'.isdigit()

(False, True)

'12345'.isdigit(), '12345pi'.isdigit(), '123.456'.isdigit()

(True, False, False)

'a'.isalnum(), '8'.isalnum()

(True, True)

'12345'.isalnum(), '12345pi'.isalnum(), '123.456'.isalnum()

(True, True, False)

'a'.isspace(), '8'.isspace(), ' '.isspace()

(False, False, True)

'A'.islower(), 'A'.isupper()

(False, True)

'a'.islower(), 'a'.isupper(), '9'.islower(), '9'.isupper()

(True, False, False, False)

'a'.upper(), 'a'.lower()

('A', 'a')

'A'.upper(), 'A'.lower()

('A', 'a')

characters = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789`~!@#$%^&*()-_+=[]{}"\'|:;,./?<> \t\n'

# isalpha
alphas = ''
for character in characters:
    if character.isalpha():
        alphas += character
print(alphas)

abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ

# isdigit
digits = ''
for character in characters:
    if character.isdigit():
        digits += character
print(digits)

0123456789

# isalnum
alphanumeric = ''
for character in characters:
    if character.isalnum():
        alphanumeric += character
print(alphanumeric)

abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789

# isspace
spaces = ''
for character in characters:
    if character.isspace():
        spaces += character
print(spaces)

😶

# isspace
spaces = []
for character in characters:
    if character.isspace():
        spaces.append(character)
print(spaces)

[' ', '\t', '\n']

# other stuff
symbols = ''
for character in characters:
    if not character.isspace() and not character.isalnum():
        symbols += character
print(symbols)

`~!@#$%^&*()-_+=[]{}"'|:;,./?<>

# upper and lower
uppers = ''
lowers = ''
for character in characters:
    if character.isupper():
        uppers += character
    elif character.islower():
        lowers += character
print(uppers)
print(lowers)

ABCDEFGHIJKLMNOPQRSTUVWXYZ
abcdefghijklmnopqrstuvwxyz

👩🏻‍🎨 No Spaces

Write a function that replaces all space characters with dashes.

def no_spaces(text: str):
    """Replace all space characters with dashes"""
    sentence = ''
    for character in text:
        if character.isspace():
            character = '-'
        sentence += character
    return sentence
        
    sentence = ''
    for character in text:
        if character.isspace():
            sentence += '-':
        else:
            sentence += character
        

def no_spaces(text):
    result = ''
    for c in text:
        if c.isspace():
            c = '-'
        result += c
    return result

print(no_spaces('BYU is the place to be.'))

BYU-is-the-place-to-be.

message = """This is a long,
multiline string.
It has multiple lines.
That is what "multiline" means. :)"""

print(message)
print()
print(no_spaces(message))

This is a long,
multiline string.
It has multiple lines.
That is what "multiline" means. :)

This-is-a-long,-multiline-string.-It-has-multiple-lines.-That-is-what-"multiline"-means.-:)

print(no_spaces('Goodbye spaces \t tabs \n and newlines'))

Goodbye-spaces---tabs---and-newlines

👨🏾‍🎨 Numbers?

Write a function that replaces every number in a string with ?

def no_numbers(text):
    """Replace every number with ?"""
    sentence = ''
    for character in text:
        if character.isdigit():
            character = 'REDACTED'
        sentence += character
    return sentence

def no_numbers(text):
    result = ''
    for char in text:
        if char.isdigit():
            result = result + '?'
        else:
            result = result + char
    return result

no_numbers('There were 7 people.')

'There were REDACTED people.'

no_numbers('15 out of 25 have more than 17.3% contamination.')

'REDACTEDREDACTED out of REDACTEDREDACTED have more than REDACTEDREDACTED.REDACTED% contamination.'

no_numbers('2 + 2 = 5, for large values of 2.')

'REDACTED + REDACTED = REDACTED, for large values of REDACTED.'

🧑🏻‍🎨 Sum of Digits

Add up all the digits found in a string.

def find_digits(text):
    """Return a list of all the digits as ints"""
    digits = []
    for char in text:
        if char.isdigit():
            digits.append(int(char))
    return digits


def add_digits(text):
    """Add all the digits found in the `text`. 
    
    >>> add_digits('123foo')
    6
    """
    return sum(find_digits(text))

def add_digits(text):
    """Add all the digits found in the `text`. 
    
    >>> add_digits('123foo')
    6
    """
    total = 0
    for c in text:
        if c.isdigit():
            total += int(c)
    return total

add_digits('123foo')

6

add_digits('10 students ate 6 oranges and 42 students ate 7 pears.')

20

🧑🏽‍🎨 Organized

Write a program that "organizes" user input.

"Organized" text means that all the characters are reordered to this sequence:

• lowercase letters
• uppercase letters
• digits
• everything else
• whitespace is removed

organize.py

Text: Hello, what is your name?
ellowhatisyournameH,?
Text: BYU is my favorite school!
ismyfavoriteschoolBYU!
Text: 3.14159 is a loose approx. for PI.
isalooseapproxforPI314159...
Text:

Key Ideas

• String iteration
• 'foo' + 'bar', 'BYU! ' * 5
• .isalpha(), .isdigit(), .isalnum(), .isspace(), .isupper(), .islower()
• .upper(), .lower()
• +=