Sliced And Diced - Python

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

>>> More Python Articles          >>> More By Vikram Vaswani, (c) Melonfire

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