¶ CH 1: Data
Lesson Notes
¶ Data Objects
In the following line of Python, which is the data and which is the algorithm?
print(“Hello World”)
The data can always be replaced with a different data of the same type, and the algorithm should still produce a similar type of result
print("Hello")
print("Goodbye")
print("Hello", "Goodbye")
Algorithms don't change (if they are valid)
Data changes value, but not type
RULE #1
Separate things that change from things that stay the same
¶ Built in Functions
print(): takes any number of arguments separated by a comma
- You can pass any number of arguments
-
print(1,2,3,'a','b','c')
-
- Arguments printed will be separated by a space and a newline added after all are printed.
A function is an algorithm with a result
In Python, algorithms are encapsulated in functions, like print().
Functions MUST ALWAYS be followed by a parenthesis, even if they are empty
print()
print() is a built-in function. You can use any of the built in functions anywhere in your program.
Data in Python is called an Object, and objects have a type and value.
Examples
- the value 65 is a type of integer
- the value "A" is a type of text
¶ type()
You can determine an object’s type with the type() command
print( type(1) )
print( type("Hello") )
¶ Strings
Computers assign numbers to to each character on the keyboard
- ‘A’: 65
<return>: 13
How does the computer know the difference between the number 65 and the letter ‘A’
This is why we need types
What about ‘1’ and 1? notice the quotes
- ’1’ actually equals the decimal value of 49
print( ord("A") ) # Every character maps to an number value
print( ord("1") ) # Even number characters
In Computer Science, we call "text” a string. A string is a list of characters (or you might say a 'string' of characters).
Strings in Python can be enclosed in:
- "A" double quotes
- 'A' single quote
- """A""" triple quote
- '''A''' single triple quote
Each character in the string has two indexes:
"Bruce's beard"
'We are the knights who say, "Ni!"'#using quotes inside quotes
¶ String Operations
We can add strings together using concatenation:
print("5"+"3") # concatenation
but types have specific operations they can perform:
print("5"-"3") #not defined for string type
You cannot subtract “2” - “2” because that operation is not defined for the string type.
You can multiply strings with the *:
print("="*5) # string multiplication
print("<"+"="*5+">") # string order of operations
Robert Frost
print("The woods are lovely, dark, and deep, But I have promises to keep, And miles to go before I sleep, And miles to go before I sleep")
How could Robert Frost have written less using Python?
print("The woods are lovely, dark, and deep, But I have promises to keep" + " And miles to go before I sleep "* 2)
¶ Numbers
-
int: a whole number (including 0)- 10, 0, -1
-
float: a fractional number- 10.5, 0.0, -0.1
¶ Operands
+, -,
* - multiplication
/ - always results in a floating point value, i.e. 0.0
** - exponent, 22 = 2**2
// - integer division, always returns an int, doesn't round, i.e 1
Division vs Integer Division
print(5/6)
print(4/4)
print(5//6)
print(4//4)
¶ Modulo
% - divide, but only care about remainder
print( 5 % 6)
print( 6 % 5)