Python 101 (part 2): If Wishes Were Pythons - Sliced And Diced (
Page 4 of 9 )
In Python-lingo,
strings are an "immutable" object type, which means that they cannot be changed
in place; the only way to alter a string is to create a new string with the
changes. Python comes with powerful built-in operators designed to make it
easier to extract subsections of a string, and thereby create new
strings.
For example, to extract the letter "b" from the string
"hobgoblin", I could use
>>> str = "hobgoblin"
>>> str[2]
'b'
>>>
This is referred to as "slicing"; the square braces [ and ]
specify the starting and ending location (or "index") for the slice. Note that
the first character is referred to by index 0.
You can extract a
substring by specifying two indices within the square braces...
>>> str = "hobgoblin"
>>> str[3:9]
'goblin'
>>>
...and watch what happens when I omit either one of the two
indices.
>>> str = "hobgoblin"
>>> str[3:]
'goblin'
>>> str[:7]
'hobgobl'
>>>
You can also use negative indices, to force Python to begin
counting from the right instead of the left.
>>> str = "hobgoblin"
>>> str[-6]
'g'
>>> str[-6:]
'goblin'
>>>
The built-in len() function can be used to calculate the
number of characters in a string,
>>> str = "hobgoblin"
>>> len(str)
9
>>>
while the "in" and "not in" operators can be used to test for
the presence of a particular character in a string. A match returns 1 (true),
while a failure returns 0 (false).
>>> str = "hobgoblin"
>>> "g" in str
1
>>> "x" in str
0
