Learn Python in One Day and Learn It Well (2015)

Appendix A: Working With Strings

Note: The notation [start, [end]] means start and end are optional parameters. If only one number is provided as the parameter, it is taken to be start.

# marks the start of a comment

‘’’ marks the start and end of a multiline comment

The actual code is in monotype font.

=> marks the start of the output

count (sub, [start, [end]])

Return the number of times the substring sub appears in the string.

This function is case-sensitive.

[Example]

# In the examples below, ‘s’ occurs at index 3, 6 and 10

# count the entire string

‘This is a string’.count(‘s’)

=> 3

# count from index 4 to end of string

‘This is a string’.count(‘s’, 4)

=> 2

# count from index 4 to 10-1
‘This is a string’.count(‘s’, 4, 10 )

=> 1

# count ‘T’. There’s only 1 ‘T’ as the function is case sensitive.

‘This is a string’.count(‘T’)

=> 1

endswith (suffix, [start, [end]])

Return True if the string ends with the specified suffix, otherwise return False.

suffix can also be a tuple of suffixes to look for.

This function is case-sensitive.

[Example]

# ’man’ occurs at index 4 to 6

# check the entire string

‘Postman’.endswith(‘man’)

=> True

# check from index 3 to end of string

‘Postman’.endswith(‘man’, 3)

=> True

# check from index 2 to 6-1

‘Postman’.endswith(‘man’, 2, 6)

=> False

# check from index 2 to 7-1

‘Postman’.endswith(‘man’, 2, 7)

=> True

# Using a tuple of suffixes (check from index 2 to 6-1)

‘Postman’.endswith((‘man’, ‘ma’), 2, 6)

=> True

find/index (sub, [start, [end]])

Return the index in the string where the first occurrence of the substring sub is found.

find() returns -1 if sub is not found.

index() returns ValueError is sub is not found.

This function is case-sensitive.

[Example]

# check the entire string

‘This is a string’.find(‘s’)

=> 3

# check from index 4 to end of string

‘This is a string’.find(‘s’, 4)

=> 6

# check from index 7 to 11-1
‘This is a string’.find(‘s’, 7,11 )

=> 10

# Sub is not found

'This is a string'.find(‘p’)

=> -1

'This is a string'.index(‘p’)

=> ValueError

isalnum()

Return true if all characters in the string are alphanumeric and there is at least one character, false otherwise.

Alphanumeric does not include whitespaces.

[Example]

‘abcd1234’.isalnum()

=> True

‘a b c d 1 2 3 4’.isalnum()

=> False

‘abcd’.isalnum()

=> True

‘1234’.isalnum()

=> True

isalpha()

Return true if all characters in the string are alphabetic and there is at least one character, false otherwise.

[Example]

‘abcd’.isalpha()

=> True

‘abcd1234’.isalpha()

=> False

‘1234’.isalpha()

=> False

‘a b c’.isalpha()

=> False

isdigit()

Return true if all characters in the string are digits and there is at least one character, false otherwise.

[Example]

‘1234’.isdigit()

=> True

‘abcd1234’.isdigit()

=> False

‘abcd’.isdigit()

=> False

‘1 2 3 4’.isdigit()

=> False

islower()

Return true if all cased characters in the string are lowercase and there is at least one cased character, false otherwise.

[Example]

‘abcd’.islower()

=> True

‘Abcd’.islower()

=> False

‘ABCD’.islower()

=> False

isspace()

Return true if there are only whitespace characters in the string and there is at least one character, false otherwise.

[Example]

‘ ’.isspace()

=> True

‘a b’.isspace()

=> False

istitle()

Return true if the string is a titlecased string and there is at least one character

[Example]

‘This Is A String’.istitle()

=> True

‘This is a string’.istitle()

=> False

isupper()

Return true if all cased characters in the string are uppercase and there is at least one cased character, false otherwise.

[Example]

‘ABCD’.isupper()

=> True

‘Abcd’.isupper()

=> False

‘abcd’.isupper()

=> False

join()

Return a string in which the parameter provided is joined by a separator.

[Example]

sep = ‘-’

myTuple = (‘a’, ‘b’, ‘c’)

myList = [‘d’, ‘e’, ‘f’]

myString = “Hello World”

sep.join(myTuple)

=> ‘a-b-c’

sep.join(myTuple)

=> ‘d-e-f’

sep.join(myString)

=> ‘H-e-l-l-o- -W-o-r-l-d’’

lower()

Return a copy of the string converted to lowercase.

[Example]

‘Hello Python’.lower()

=> ‘hello python’

replace(old, new[, count])

Return a copy of the string with all occurrences of substring old replaced by new.

count is optional. If given, only the first count occurrences are replaced.

This function is case-sensitive.

[Example]

# Replace all occurences

‘This is a string’.replace(‘s’, ‘p’)

=> 'Thip ip a ptring'

# Replace first 2 occurences

‘This is a string’.replace(‘s’, ‘p’, 2)

=> 'Thip ip a string'

split([sep [,maxsplit]])

Return a list of the words in the string, using sep as the delimiter string.

sep and maxsplit are optional.

If sep is not given, whitespace is used as the delimiter.

If maxsplit is given, at most maxsplit splits are done.

This function is case-sensitive.

[Example]

‘’’

Split using comma as the delimiter

Notice that there’s a space before the words ‘is’, ‘a’ and ‘string’ in the output.

‘’’

‘This, is, a, string’.split(‘,’)

=> ['This', ' is', ' a', ' string']

# Split using whitespace as delimiter

‘This is a string’.split()

=> ['This', 'is', 'a', 'string']

# Only do 2 splits

‘This, is, a, string’.split(‘,’ 2)

=> ['This', ' is', ' a, string']

splitlines ([keepends])

Return a list of the lines in the string, breaking at line boundaries.

Line breaks are not included in the resulting list unless keepends is given and true.

[Example]

# Split lines separated by \n

‘This is the first line.\nThis is the second line’.splitlines()

=> ['This is the first line.', 'This is the second line.']

# Split multi line string (e.g. string that uses the ‘’’ mark)

‘’’This is the first line.

This is the second line.’’’.splitlines()

=> ['This is the first line.', 'This is the second line.']

# Split and keep line breaks

'This is the first line.\nThis is the second line.'.splitlines(True)

=> ['This is the first line.\n', 'This is the second line.']

‘’’This is the first line.

This is the second line.’’’.splitlines(True)

=> ['This is the first line.\n', 'This is the second line.']

startswith (prefix[, start[, end]])

Return True if string starts with the prefix, otherwise return False.

prefix can also be a tuple of prefixes to look for.

This function is case-sensitive.

[Example]

# ’Post’ occurs at index 0 to 3

# check the entire string

‘Postman’.startswith(‘Post’)

=> True

# check from index 3 to end of string

‘Postman’.startswith(‘Post’, 3)

=> False

# check from index 2 to 6-1

‘Postman’.startswith(‘Post’, 2, 6)

=> False

# check from index 2 to 6-1

‘Postman’.startswith(‘stm’, 2, 6)

=> True

# Using a tuple of prefixes (check from index 3 to end of string)

‘Postman’.startswith((‘Post’, ‘tma’), 3)

=> True

strip ([chars])

Return a copy of the string with the leading and trailing characters char removed.

If char is not provided, whitespaces will be removed.

This function is case-sensitive.

[Example]

# Strip whitespaces

‘ This is a string ’.strip()

=> 'This is a string'

# Strip ‘s’. Nothing is removed since ‘s’ is not at the start or end of the string

'This is a string'.strip('s')

=> 'This is a string'

# Strip ‘g’.

‘This is a string’.strip(‘g’)

=> ‘This is a strin’

upper()

Return a copy of the string converted to uppercase.

[Example]

‘Hello Python’.upper()

=> ‘HELLO PYTHON