Lesson 5 · Python data types deep dive

Python Strings Explained: Slicing, Methods & f-Strings | Data Types #5

Video five of the twelve-part series: str, the largest built-in type by method count, and the most-used type in nearly every real Python program. Every…

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Python Data Types Deep-Dive, Video 5: Strings (str)#

Video five of the twelve-part series: str, the largest built-in type by method count, and the most-used type in nearly every real Python program.
Every literal form, indexing and slicing, and all forty-seven public str methods, one at a time.
This is the longest video in the series. Let's get into it.

Part 1: What Makes str Different#

greeting = 'Hello'
print(type(greeting))
print(len(greeting))
upper_version = greeting.upper()
print(greeting)
print(upper_version)

<class 'str'>
5
Hello
HELLO

Part 2: String Literals#

single = 'single quotes'
double = "double quotes, letting 'these' through"
triple = '''a genuine
multi-line string'''
escaped = 'Line one\nLine two\tTabbed'
raw = r'C:\Users\name\no_escapes_here'
print(single, double, sep=' | ')
print(triple)
print(escaped)
print(raw)

single quotes | double quotes, letting 'these' through
a genuine
multi-line string
Line one
Line two	Tabbed
C:\Users\name\no_escapes_here

name = 'Ana'
age = 29
print(f'{name} is {age} years old')
print(f'{name.upper()} is {age * 2} in dog years, sort of')
print('concatenated ' + 'with plus')
print('implicit' ' concatenation')

Ana is 29 years old
ANA is 58 in dog years, sort of
concatenated with plus
implicit concatenation

Part 3: Indexing and Slicing#

word = 'Python'
print(word[0])
print(word[-1])
print(word[1:4])
print(word[:3])
print(word[3:])
print(word[::-1])
print(word[::2])

P
n
yth
Pyt
hon
nohtyP
Pto

Part 4: Case-Changing Methods#

text = 'the Quick BROWN fox'
print(text.upper())
print(text.lower())
print(text.capitalize())
print(text.title())
print(text.swapcase())
print('STRASSE'.casefold())
print('STRASSE'.lower())

THE QUICK BROWN FOX
the quick brown fox
The quick brown fox
The Quick Brown Fox
THE qUICK brown FOX
strasse
strasse

Part 5: Case-Checking Methods#

print('HELLO'.isupper())
print('Hello'.isupper())
print('hello'.islower())
print('Hello World'.istitle())
print('Hello world'.istitle())
print('123'.isupper())

True
False
True
True
False
False

Part 6: Alignment and Padding Methods#

word = 'hi'
print(f'[{word.center(10)}]')
print(f'[{word.center(10, chr(42))}]')
print(f'[{word.ljust(10)}]')
print(f'[{word.rjust(10)}]')
print('42'.zfill(5))
print('-42'.zfill(5))

[    hi    ]
[****hi****]
[hi        ]
[        hi]
00042
-0042

Part 7: Stripping Methods#

messy = '   padded text   '
print(f'[{messy.strip()}]')
print(f'[{messy.lstrip()}]')
print(f'[{messy.rstrip()}]')
print('xxxhelloxxx'.strip('x'))
print('***important***'.strip('*'))

[padded text]
[padded text   ]
[   padded text]
hello
important

Part 8: Searching Methods#

sentence = 'the quick brown fox jumps over the lazy dog'
print(sentence.find('the'))
print(sentence.rfind('the'))
print(sentence.find('cat'))
print(sentence.index('the'))
print(sentence.find('brown', 10))

sentence = 'the quick brown fox'
try:
    sentence.index('cat')
except ValueError as e:
    print(f'Caught: {e}')

Caught: substring not found

Part 9: count()#

text = 'mississippi'
print(text.count('s'))
print(text.count('ss'))
print(text.count('i'))
print(text.count('iss'))

Part 10: startswith() and endswith()#

filename = 'report_final.pdf'
print(filename.startswith('report'))
print(filename.endswith('.pdf'))
print(filename.endswith(('.pdf', '.docx', '.txt')))
print(filename.endswith('.csv'))

True
True
True
False

Part 11: Splitting Methods#

csv_row = 'apple,banana,cherry,date'
print(csv_row.split(','))
print(csv_row.split(',', 2))
print(csv_row.rsplit(',', 1))
print('  spaced   out   words  '.split())

['apple', 'banana', 'cherry', 'date']
['apple', 'banana', 'cherry,date']
['apple,banana,cherry', 'date']
['spaced', 'out', 'words']

multiline = 'line one\nline two\r\nline three'
print(multiline.splitlines())
print(multiline.splitlines(keepends=True))

['line one', 'line two', 'line three']
['line one\n', 'line two\r\n', 'line three']

url = 'user@example.com'
print(url.partition('@'))
print(url.rpartition('@'))
path = 'a/b/c/d'
print(path.rpartition('/'))

('user', '@', 'example.com')
('user', '@', 'example.com')
('a/b/c', '/', 'd')

Part 12: join()#

words = ['the', 'quick', 'brown', 'fox']
print(' '.join(words))
print(', '.join(words))
print(''.join(words))
print('-'.join(str(n) for n in range(5)))

the quick brown fox
the, quick, brown, fox
thequickbrownfox
0-1-2-3-4

Part 13: replace()#

text = 'the cat sat on the mat'
print(text.replace('the', 'THE'))
print(text.replace('the', 'THE', 1))
print(text.replace('at', 'og'))

THE cat sat on THE mat
THE cat sat on the mat
the cog sog on the mog

Part 14: Character Classification Methods#

print('Python3'.isalnum())
print('Python 3'.isalnum())
print('Python'.isalpha())
print('123'.isdigit())
print('123'.isdecimal())
print('\u00b2'.isdigit())
print('\u00b2'.isdecimal())
print('\u00bd'.isnumeric())

True
False
True
True
True
True
False
True

print('   '.isspace())
print('\t\n'.isspace())
print('hello'.isascii())
print('caf\u00e9'.isascii())
print('hello world'.isprintable())
print('hello\n'.isprintable())
print('variable_name'.isidentifier())
print('2variable'.isidentifier())
print(''.isalnum())

True
True
True
False
True
False
True
False
False

Part 15: format() and format_map()#

template = '{} is {} years old'
print(template.format('Ana', 29))
named_template = '{name} scored {score} points'
print(named_template.format(name='Sam', score=95))
indexed_template = '{1} comes before {0}'
print(indexed_template.format('second', 'first'))
print('{:.2f}'.format(3.14159))

Ana is 29 years old
Sam scored 95 points
first comes before second
3.14

data = {'name': 'Chen', 'role': 'engineer', 'extra': 'unused'}
template = '{name} works as an {role}'
print(template.format_map(data))

Chen works as an engineer

Part 16: translate() and maketrans()#

table = str.maketrans('aeiou', 'AEIOU')
print('the quick brown fox'.translate(table))
remove_table = str.maketrans('', '', 'aeiou')
print('the quick brown fox'.translate(remove_table))
rot13_table = str.maketrans(
    'abcdefghijklmnopqrstuvwxyz',
    'nopqrstuvwxyzabcdefghijklm'
)
print('hello'.translate(rot13_table))

thE qUIck brOwn fOx
th qck brwn fx
uryyb

Part 17: encode()#

text = 'caf\u00e9'
print(text.encode('utf-8'))
print(text.encode('ascii', errors='ignore'))
print(text.encode('ascii', errors='replace'))
try:
    text.encode('ascii')
except UnicodeEncodeError as e:
    print(f'Caught: {e}')

b'caf\xc3\xa9'
b'caf'
b'caf?'
Caught: 'ascii' codec can't encode character '\xe9' in position 3: ordinal not in range(128)

Part 18: expandtabs()#

row = 'name\tage\tcity'
print(row)
print(repr(row.expandtabs()))
print(repr(row.expandtabs(4)))
print(repr(row.expandtabs(2)))

name	age	city
'name    age     city'
'name    age city'
'name  age city'

Part 19: removeprefix() and removesuffix()#

filename = 'test_report.txt'
print(filename.removeprefix('test_'))
print(filename.removeprefix('nope_'))
print(filename.removesuffix('.txt'))
print(filename.removesuffix('.pdf'))

report.txt
test_report.txt
test_report
test_report.txt

Part 20: Immutability in Practice#

word = 'hello'
try:
    word[0] = 'H'
except TypeError as e:
    print(f'Caught: {e}')
word = 'H' + word[1:]
print(word)

Caught: 'str' object does not support item assignment
Hello

Part 21: Common Patterns and Pitfalls#

words = ['this', 'is', 'genuinely', 'slow']
result = ''
for word in words:
    result += word + ' '
print(result.strip())
fast_result = ' '.join(words)
print(fast_result)

this is genuinely slow
this is genuinely slow

print('10' < '9')
print('apple' < 'banana')
print('Apple' < 'apple')
print(sorted(['10', '9', '2', '1']))
print(sorted([10, 9, 2, 1]))

True
True
True
['1', '10', '2', '9']
[1, 2, 9, 10]

Wrap-Up: What You Learned#

String literals, escape sequences, raw strings, f-strings, and indexing/slicing.
Case methods: upper, lower, capitalize, title, swapcase, casefold, isupper, islower, istitle.
Padding and stripping: center, ljust, rjust, zfill, strip, lstrip, rstrip.
Searching and counting: find, rfind, index, rindex, count, startswith, endswith.
Splitting and joining: split, rsplit, splitlines, partition, rpartition, join, replace.
All nine character classification methods, from isalnum to isidentifier.
Templating with format and format_map, translate and maketrans, encode, expandtabs, removeprefix, and removesuffix.
Immutability, efficient string building with join, and lexicographic versus numeric sorting.
That's all forty-seven public str methods covered. Next up: list, the workhorse mutable sequence type.

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