Introduction to Python

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Math and String Operators

+, -, *, /: math operators

Math operators behave as you might expect.

var_int = 5
var2_float = 10.3

var3_float = var_int + var2_float    # int plus a float:  15.3, a float

var4_float = var3_float - 0.3    # float minus a float:  15.0, a float

var5_float = var4_float / 3      # float divided by an int:  5.0, a float

identifying type through an operation

Every operation or function call results in a predictable type.

With two integers, the result is integer. If a float is involved, it's always flot.

vari = 7
vari2 = 3
varf = 3.0

var3 = var * var2      # 35, an int.

var4 = var + var2      # 10.0, a float

When an integer is divided into another integer, the result is always a float.

var = 7
var2 = 3

var3 = var / var2      # 2.3333, a float

• we usually don't worry too much about ints vs. floats, because they work well together
• however, we do want to start thinking about type

** exponentiation operator

The exponentiation operator (**) raises its left operand to the power of its right operand and returns the result as a float or int.

var = 11 ** 2     # "eleven raised to the 2nd power (squared)"
print(var)        # 121

var = 3 ** 4
print(var)        # 81

% Modulus Operator

The modulus operator (%) shows the remainder that would result from division of two numbers.

var = 11 % 2      # "eleven modulo two"
print(var)        # 1   (11/2 has a remainder of 1)


var2 = 10 % 2     # "ten modulo two"
print(var2)       # 0   (10/2 divides evenly:  remainder of 0)

• modulus shows the remainder of a division
• modulus with 2 is useful because it shows us whether a number is even or odd

+ operator with strings: concatenation

The plus operator (+) with two strings returns a concatenated string.

aa = 'Hello, '
bb = 'World!'

cc = aa + bb     # 'Hello, World!'

Note that this is the same operator (+) that is used with numbers for summing. Python uses the type of the operands (values on either side of the operator) to determine behavior and result.

* operator with one string and one integer: string repetition

The "string repetition operator" (*) creates a new string with the operand string repeated the number of times indicated by the other operand:

aa = '!'
bb = 5

cc = aa * bb       # '!!!!!!'

Note that this is the same operator (*) that is used with numbers for multiplication. Python uses the type of the operands to determine behavior and result.

python's "overloaded" operator +

Object types determine behavior.

int or float "added" to int or float: addition

tt = 5            # assign an integer value to tt
zz = 10.0         # assign a float value to zz

qq = tt + zz      # compute 5 plus 10 and assign float 15.0 to qq

str "added" to str: concatenation

kk = '5'          # assign a str value (quotes mean str) to kk
rr = '10.0'       # assign a str value to rr

mm = kk + rr      # concatenate '5' and '10.0'
                  # to construct a new str object, assign to mm

print(mm)         # '510.0'

• the plus operator serves double duty depending on what types are used
• we call this type of behavior 'polymorphism'

python's "overloaded" operator *

Again, object types determine behavior.

int or float "multipled" by int or float: multiplication

tt = 5            # assign an integer value to tt
zz = 10           # assign an integer value to zz

qq = tt * zz      # compute 5 times 10 and assign integer 50 to qq
print(qq)         # 50, an int

str "multiplied" by int: string repetition

aa = '5'
bb = 3

cc = aa * bb      # '555'

• once again, object types determine what is possible (and not possible) in the language
• this is why it's so important to know the type of every variable