Download Python 8: Fun with strings

OCR GCSE Computing
Python programming
8: Fun with strings
OCR Computing GCSE
© Hodder Education 2013
Slide 1
Python 8: Fun with strings
A string is a sequence of characters.
A string is a Python object.
As such it has methods.
A string is given in quotes:
‘This is a string’
OCR Computing GCSE
© Hodder Education 2013
Slide 2
Python 8: Fun with strings
You can use arithmetic operators
on strings.
Concatenation is the joining of
strings.
Use the + operator to join strings.
Use the * operator to make
multiple copies of strings.
OCR Computing GCSE
© Hodder Education 2013
Slide 3
Python 8: Fun with strings
Strings have ‘methods’. This is the built-in things that they can
do.
Methods of objects are referenced by the ‘dot’ notation.
For example, to make a string upper case, use the upper
method.
string.upper()
Notice the brackets in case you need to add arguments.
Remember: Strings are immutable. This means once they
have been created, they cannot be changed. But, you can
copy them and examine them.
OCR Computing GCSE
© Hodder Education 2013
Slide 4
Python 8: Fun with strings
A few string methods:
OCR Computing GCSE
© Hodder Education 2013
Slide 5
Python 8: Fun with strings
The ‘in’ operator
This useful Python operator can check if something is in a sequence, e.g.
a string, a list or a tuple. It saves writing a lot of searching code.
OCR Computing GCSE
© Hodder Education 2013
Slide 6
Python 8: Fun with strings
Indexing strings
Each letter (character) in a string has a numbered position.
We can demonstrate this in the following program:
This program finds the
length of a word that is
input, then iterates through
the word printing each letter
in turn on a new line.
OCR Computing GCSE
© Hodder Education 2013
Slide 7
Python 8: Fun with strings
You can access any letter in a word by using its index. Remember that
Python starts counting at 0. So, the first letter of ‘word’ is word[0]. You can
use negative numbers to count back from the last letter, so word[-1] is the
last letter.
So, suppose
word=‘hello’
word[0] is ‘h’
word[1] is ‘e’
OCR Computing GCSE
© Hodder Education 2013
Slide 8
Python 8: Fun with strings
Slicing
You can access a portion of a string.
You are not restricted to one letter at a time.
You just need to specify the start position and the end position.
You can use positive or negative positions, or a mixture of the two.
OCR Computing GCSE
© Hodder Education 2013
Slide 9