1. Intro to CS Nov 2, 2015

2. Today Python data types and operations Casting data types
Built-in functions for keyboard input

3. Four Python data types int: age = 20 float: pi = 3.14159 String:
name = ‘Alice’
Boolean:
isCold = True

4. Doing arithmetic + Addition - Subtraction * Multiplication / Division
>>> 5/2 = 2.5
% Modulus
How to determine an integer is even or odd?
// Floor division
>>> 5//2 = 2
** Exponent
>>> 5**3 = 125

5. Data types and operators
Numeric types can use all arithmetic operators
If mixing string and numeric, be careful !!!
print(3+5.5) # ok. Output: 8.5
print(3+’5.5’) # error: unsupported type
print(‘3’+’5.5’) # ok. String operation
# output: 35.5
print( ‘Hi’*5) #ok. Output: HiHiHiHiHi
print(‘Hi’+5) # error.

6. Built-in functions for type conversion
Type conversion is also called type casting
int(x): convert x to a integer
example: int(‘5’)
float(x): convert x to a decimal
example: float(‘2.8’)
str(x): convert x to a string
example: str(5)

7. Type conversion example
print(3+’5’) #error
print(3+int(‘5’)) #ok
print(‘Hi’ + 5) #error
print(‘Hi’ + str(5)) #ok. Output: Hi5

8. Built-in function for keyboard input
Program stops, waits for the user to type something.
After user types something and presses Enter, the
program resumes and returns what the user typed as a
string.
Example
print(“Please enter your username: “)
x=raw_input()
print(“You just entered: “, x)

9. Built-in function for keyboard input (cont’)
The Zen of Python: simple is better than complex
print(“Please enter your username: “)
x=raw_input()
print(“You just entered: “, x)
Can be rewritten as:
x=raw_input(“Please enter your username: “)

10. Built-in function for keyboard input (cont’)
Question: What is the total price to buy 5 books if each costs $10?
print("One book costs $10")
num_books=input(“How many books you will buy: “)
price = num_books*10
print(“Your total price = “, price, “dollars”)

11. Built-in function for keyboard input (cont’)
Question: input() always returns a string. What if I need a number?
x=raw_input(“How many books you will buy: “)
num_books = int(x) #use int() to convert
# string to int
price = num_books*10
print(“Your total price = “, price)

12. Summary Python data types: int, float, string, boolean
Arithmetic operations
Casting data types: int(), float(), str()
keyboard input()