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)

'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()

(True, 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):
    """Replace all space characters with dashes"""
    new_text = ''
    for char in text:
        if char.isspace():
            char = '-'
        new_text += char
    return new_text

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 ?"""
    new_text = ''
    for char in text:
        if char.isdigit():
            char = '?'
        new_text += char
    return new_text

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 ? people.'

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

'?? out of ?? have more than ??.?% contamination.'

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

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

🧑🏻‍🎨 Sum of Digits

Add up all the digits found in a string.

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

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

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()
• +=