1. OCR Computing GCSE © Hodder Education 2013 Slide 1 OCR GCSE Computing Python programming 8: Fun with strings

2. OCR Computing GCSE © Hodder Education 2013 Slide 2 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’

3. OCR Computing GCSE © Hodder Education 2013 Slide 3 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.

4. OCR Computing GCSE © Hodder Education 2013 Slide 4 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.

5. OCR Computing GCSE © Hodder Education 2013 Slide 5 Python 8: Fun with strings A few string methods:

6. OCR Computing GCSE © Hodder Education 2013 Slide 6 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.

7. OCR Computing GCSE © Hodder Education 2013 Slide 7 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.

8. OCR Computing GCSE © Hodder Education 2013 Slide 8 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’

9. OCR Computing GCSE © Hodder Education 2013 Slide 9 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.