Strings

Definition

String type is immutable. Need to allocate new strings when slicing or concatenating. Try to write values from the back, instead of front. Reduce space complexity by using the string itself instead of brute force O(n) solutions.

Basic operations

t = 'My first string'
s = ' first '
print(f'in: {s in t}')
print(f'strip(): |{s}| -> |{s.strip()}|')
print(f'startswith(): {t.startswith("M")}')
print(f'endswith(): {t.endswith("ing")}')
print(f'STR.split(SEP): {t.split(" ")}')
print(f'SEP.join(LIST): {"/".join(["hey", "ho", "O"])}')
print(f'STR.lower(): {t.lower()}')
mystr = f'Testing this string: {t}'
print(mystr)

in: True
strip(): | first | -> |first|
startswith(): True
endswith(): True
STR.split(SEP): ['My', 'first', 'string']
SEP.join(LIST): hey/ho/O
STR.lower(): my first string
Testing this string: My first string

# all methods related to string
dir(s)

['__add__',
 '__class__',
 '__contains__',
 '__delattr__',
 '__dir__',
 '__doc__',
 '__eq__',
 '__format__',
 '__ge__',
 '__getattribute__',
 '__getitem__',
 '__getnewargs__',
 '__gt__',
 '__hash__',
 '__init__',
 '__init_subclass__',
 '__iter__',
 '__le__',
 '__len__',
 '__lt__',
 '__mod__',
 '__mul__',
 '__ne__',
 '__new__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__rmod__',
 '__rmul__',
 '__setattr__',
 '__sizeof__',
 '__str__',
 '__subclasshook__',
 'capitalize',
 'casefold',
 'center',
 'count',
 'encode',
 'endswith',
 'expandtabs',
 'find',
 'format',
 'format_map',
 'index',
 'isalnum',
 'isalpha',
 'isascii',
 'isdecimal',
 'isdigit',
 'isidentifier',
 'islower',
 'isnumeric',
 'isprintable',
 'isspace',
 'istitle',
 'isupper',
 'join',
 'ljust',
 'lower',
 'lstrip',
 'maketrans',
 'partition',
 'replace',
 'rfind',
 'rindex',
 'rjust',
 'rpartition',
 'rsplit',
 'rstrip',
 'split',
 'splitlines',
 'startswith',
 'strip',
 'swapcase',
 'title',
 'translate',
 'upper',
 'zfill']

Useful tips

convert string to number in a given base

from functools import reduce
from string import hexdigits
def num_to_int (num_as_string, base):
    return reduce(lambda x,c: x * base + hexdigits.index(c.lower()), num_as_string, 0)
num_to_int('613', 7)

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