4. strings (python).md

STRINGS

(properties: iterable, immutable)

create a string

s = str(42)         # convert another data type into a string
s = 'I like you'

examine a string

s[0]                # returns 'I'
len(s)              # returns 10

string slicing like lists

s[:6]               # returns 'I like'
s[7:]               # returns 'you'
s[-1]               # returns 'u'

basic string methods (does not modify the original string)

s.lower()           # returns 'i like you'
s.upper()           # returns 'I LIKE YOU'
s.startswith('I')   # returns True
s.endswith('you')   # returns True
s.isdigit()         # returns False (returns True if every character in the string is a digit)
s.find('like')      # returns index of first occurrence (2), but doesn't support regex
s.find('hate')      # returns -1 since not found
s.replace('like','love')    # replaces all instances of 'like' with 'love'

split a string into a list of substrings separated by a delimiter

s.split(' ')        # returns ['I','like','you']
s.split()           # same thing
s2 = 'a, an, the'
s2.split(',')       # returns ['a',' an',' the']

join a list of strings into one string using a delimiter

stooges = ['larry','curly','moe']
' '.join(stooges)   # returns 'larry curly moe'

concatenate strings

s3 = 'The meaning of life is'
s4 = '42'
s3 + ' ' + s4       # returns 'The meaning of life is 42'
s3 + ' ' + str(42)  # same thing

remove whitespace from start and end of a string

s5 = '  ham and cheese  '
s5.strip()          # returns 'ham and cheese'

string substitutions: all of these return 'raining cats and dogs'

'raining %s and %s' % ('cats','dogs')                       # old way
'raining {} and {}'.format('cats','dogs')                   # new way
'raining {arg1} and {arg2}'.format(arg1='cats',arg2='dogs') # named arguments

string formatting

more examples: http://mkaz.com/2012/10/10/python-string-format/

'pi is {:.2f}'.format(3.14159)      # returns 'pi is 3.14'

normal strings versus raw strings

print 'first line\nsecond line'     # normal strings allow for escaped characters
print r'first line\nfirst line'     # raw strings treat backslashes as literal characters

get last three characters

i[-3:]

Replace some character from end of a string

http://stackoverflow.com/questions/3675318/how-to-replace-the-some-characters-from-the-end-of-a-string

def replace_last(source_string, replace_what, replace_with):
    head, sep, tail = source_string.rpartition(replace_what)
    return head + replace_with + tail

s = "123123"
r = replace_last(s, '2', 'x')
print r # 1231x3