Day 1 – Lesson 4 Beginning Functions

1. Day 1 – Lesson 4Beginning Functions Python Mini-Course University of Oklahoma Department of Psychology Python Mini-Course: Day 1 - Lesson 4

2. Lesson objectives • State the purpose of functions and modules in Python • Use built-in functions • Import modules and use imported functions • Create custom void functions • Discuss the concept of variable scope Python Mini-Course: Day 1 - Lesson 4

3. Functions • Function • A named sequence of statements that performs a computation or action • Functions are called by name • Most functions accept inputs (arguments) • Some functions return results (return value) Python Mini-Course: Day 1 - Lesson 4

4. Functions • We’ve already seen some functions: • type() • Type casting functions • int(), float(), str() Python Mini-Course: Day 1 - Lesson 4

5. Modules • Module • A file that contains a collection of related functions • Python has hundreds of standard modules • These are known as the Python Standard Library (http://docs.python.org/library/) • You can also create and use add-in modules Python Mini-Course: Day 1 - Lesson 4

6. Using import • To use a module, you first have to import it into your namespace • To import the entire moduleimport module_name • To import specific functionsfrom module_name import function_name Python Mini-Course: Day 1 - Lesson 4

7. The math module • The standard math module includes: • Number-theoretic and representation functions • Power and logarithmic functions • Trigonometric functions • Hyperbolic functions • Angular conversion • Constants Python Mini-Course: Day 1 - Lesson 4

8. Using the math module import math degrees = 45 radians = degrees / 360.0 \ * 2 * math.pi print math.sin(radians) x = math.sin(degrees / 360.0 \ * 2 * math.pi) Python Mini-Course: Day 1 - Lesson 4

9. Dot notation • Why did we use math.sin() instead of just sin()? • Try this: print sin(radians) • Dot notation allows the Python interpreter to organize and divide the namespace Python Mini-Course: Day 1 - Lesson 4

10. More on Importing from math import * print sin(2) • Be careful when using the import * command. It can easily lead to namespace conflicts. Python Mini-Course: Day 1 - Lesson 4

11. Creating your own functions • You have to define the function • Example: def print_lyrics(): print "I'm a lumberjack, and I'm okay." print "I sleep all night and I work all day." Python Mini-Course: Day 1 - Lesson 4

12. Composing functions def repeat_lyrics(): print_lyrics() print_lyrics() repeat_lyrics() Python Mini-Course: Day 1 - Lesson 4

13. Functions with arguments def print_twice(in_text): print in_text print in_text print_twice(‘Spam’) print_twice(‘Spam’*4) Python Mini-Course: Day 1 - Lesson 4

14. Variable scope • Scope • The enclosing context where values and expressions are associated (partition in namespace) • Variables inside functions are local Python Mini-Course: Day 1 - Lesson 4

15. Variable scope def cat_string(part1, part2): cat = part1 + part2 print cat cat_string(‘This ‘, ‘works’) print cat Python Mini-Course: Day 1 - Lesson 4

16. Documentation • You can document functions in the code immediately after the function header • Example: func_doc.py Python Mini-Course: Day 1 - Lesson 4

17. Before next time • Practice creating and using your own functions (try the exercises on pp 26-28) • Practice using the math module (see http://docs.python.org/library/math.html for documentation) Python Mini-Course: Day 1 - Lesson 4