Knowledge Base Strings

String manipulation (operators, functions)

s[2], len(s), s+t, s[2:4], s in t, s.strip(), s.lower(), s.upper()

s.startswith(prefix), s.endswith(suffix),

‘some, and’.split(‘,’),

3 * ‘01’,

>>> ','.join(('word1', 'word2'))
'word1,word2'
>>> 'apples,pies'.split(',')
['apples', 'pies']
>>> 'first: {fname}, last: {lname}'.format(fname='Julie', lname='Frankopone')
'first: Julie, last: Frankopone'
# Test if value is alphanumeric.
>>> a = 'a2'
>>> a.isalnum()
True

isalpha() Returns True if the string consists only of letters and isn’t blank

isalnum() Returns True if the string consists only of letters and numbers and is not blank

Strings are immutable

Operations like s = s[1:] or s +=’ 123’ imply creating a new array of characters that is then assigned back to s. Or alternatively use list().

String immutability also means O(n**2) time to concatenate a character to a string n times in a for loop (unless when some Python built-ins improve it to O(n)).

Keep in mind that updating from the front is more expensive that writing to the end (and reversing the result when needed as the last operation).