• str is immutable

  • str methods create a new modified str

Whenever you call a method on string, it will not change that string, but it will generate a new one. You can capture this newly generated string:

>>> text = 'Alice'
>>> result = text.upper()
>>>
>>> print(result)
ALICE
>>>
>>> print(text)
Alice

You can also assign to the same variable, which will give you an impression that this modified string, but in fact that is a new object to which text identifier will point:

>>> text = 'Alice'
>>> text = text.upper()
>>>
>>> print(text)
ALICE

6.8.1. Memory

../../_images/type-str-memory-1.png
../../_images/type-str-memory-2.png
../../_images/type-str-memory-3.png
../../_images/type-str-immutable.png

6.8.2. Value Check

  • Use == to check if strings are equal

This is valid way to check str value:

>>> name = 'Alice'
>>>
>>> name == 'Alice'
True

6.8.3. Length

  • Builtin len() returns the length of a string

6.8.4. Method Chaining

>>> name = 'Angus MacGyver 3'
>>> result = name.lower().replace('mac', 'mc').replace('3', 'III').strip().title()

>>> name = 'Angus MacGyver 3'
>>>
>>> result = (
...     name
...     .lower()
...     .replace('mac', 'mc')
...     .replace('3', 'III')
...     .replace('2', 'II')
...     .replace('1', 'I')
...     .strip()
...     .title()
... )

6.8.5. Use Case - 1

>>> DATA = 'ul. pANA tWARdoWSKiego 3'
>>>
>>> result = (
...     DATA
...
...     # Normalize
...     .upper()
...
...     # Remove whitespace control chars
...     .replace('\n', ' ')
...     .replace('\t', ' ')
...     .replace('\v', ' ')
...     .replace('\f', ' ')
...
...     # Remove whitespaces
...     .replace('    ', ' ')
...     .replace('   ', ' ')
...     .replace('  ', ' ')
...
...     # Remove special characters
...     .replace('$', '')
...     .replace('@', '')
...     .replace('#', '')
...     .replace('^', '')
...     .replace('&', '')
...     .replace('.', '')
...     .replace(',', '')
...     .replace('|', '')
...
...     # Remove prefixes
...     .removeprefix('ULICA')
...     .removeprefix('UL')
...     .removeprefix('OSIEDLE')
...     .removeprefix('OS')
...
...     # Substitute
...     .replace('3', 'III')
...     .replace('2', 'II')
...     .replace('1', 'I')
...
...     # Format output
...     .title()
...     .replace('Iii', 'III')
...     .replace('Ii', 'II')
...     .strip()
... )
>>>
>>> print(result)
Pana Twardowskiego III