Day 2 – Lesson 7 Conditionals and Loops

1. Day 2 – Lesson 7Conditionals and Loops Python Mini-Course University of Oklahoma Department of Psychology Python Mini-Course: Day 2 - Lesson 7

2. Lesson objectives • Use conditional statements in Python, including the “if”, “if…else”, and “if…elif” statements • Use Boolean logic to create complex conditionals • Use the “for” statement to create loops Python Mini-Course: Day 2 - Lesson 7

3. Conditional execution (if…) • Syntax: if condition: do_something • Condition must be statement that evaluates to a boolean value (True or False) Python Mini-Course: Day 2 - Lesson 7

4. Example:Checking user input x = raw_input("X? ") if x.isdigit(): print "You input a number" Python Mini-Course: Day 2 - Lesson 7

5. Alternative execution • Syntax: if condition: do_something else: do_alternative Python Mini-Course: Day 2 - Lesson 7

6. Example:Checking user input x = raw_input("x? ") if x.isdigit(): print "You input a number" else: print "Please input a number\ next time" Python Mini-Course: Day 2 - Lesson 7

7. Example:Avoiding division by zero x = int(raw_input("x? ")) y = int(raw_input("y? ")) if y <> 0: print x / y else: print "Attempted division by\ zero" Python Mini-Course: Day 2 - Lesson 7

8. Chained conditionals • Syntax: if condition: do_something elif condition: do_alternative1 else: do_alternative2 Python Mini-Course: Day 2 - Lesson 7

9. Example: x = int(raw_input("x? ")) y = int(raw_input("y? ")) if x < y: print 'x is less than y' elif x > y: print 'x is greater than y' else: print 'x and y are equal' Python Mini-Course: Day 2 - Lesson 7

10. Notes on conditionals • You have to have at least one statement inside each branch but you can use the pass command while stubbing if x < 0: pass #Handle neg values Python Mini-Course: Day 2 - Lesson 7

11. Notes on conditionals • You can have as many elif branches as you need • This replaces the select and switch commands in other languages • Conditionals can be nested • Example: nested.py Python Mini-Course: Day 2 - Lesson 7

12. Complex condition statements • Use Boolean logic operators and, or, and not to chain together simple conditions • Example: boolean.py Python Mini-Course: Day 2 - Lesson 7

13. The for loop • Used to repeat a section of code a set number of times • Syntax: for target in sequence: do_statements Python Mini-Course: Day 2 - Lesson 7

14. Example: (power.py) def power(base, exponent): val = base for x in range(1,exponent): val = val * base print val power(3,4) Python Mini-Course: Day 2 - Lesson 7

15. Example: (power.py) def power(base, exponent): val = base for x in range(1,exponent): print x, val val = val * base print val Python Mini-Course: Day 2 - Lesson 7

16. Example: (power.py) def power(base, exponent): val = base for x in range(1,exponent): print x, val val = val * base print val Python Mini-Course: Day 2 - Lesson 7

17. Exercises • Find a major bug in the power function and correct it • Add a docstring to the power function • Add type checking and value checking to the power function Python Mini-Course: Day 2 - Lesson 7