JamCoders

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JamCoders Day 1 Lecture 2

Boaz Barak

Operations (integral types)

# Python things can be combined using arithmetic operators
1 + 1

2

# The result of arithmetic operations can be assigned to variables
x = 10. - 5.3
y=5
z=x+y
z

9.7

# The result of an arithmetic operation WILL NOT CHANGE the variable contents
x*2

9.4

# as you can see here
x

4.7

# To change the value of a variable, we assign to it a new value
x = x * 2
x

18.8

# An example of floating point division
4.3 / 2.0

2.15

# An example of division of integers
16 / 6

2.6666666666666665

# Integer division
16 // 6

2

# An example of "modulus" or "mod" or "finding the remainder"
4 % 3

1

# What is the answer?
8 % 3

2

# How about now?
10 % 4

# How about now?
10 % 2

0

# And now?
143 % 5

x = 1
x = x + 1
x

x = 1
x += 1 # This is equivalent to "x = x + 1"
x

x = 10
x -= 5
x

x = 60
x *= 50
x

3000

x = 100
x /= 10
x
type(x)

x = 100
x //= 10
x

10

Difference between = and ==

x = 5: Assign the value 5 to the variable x

x==5: Is True if x equals to 5 already and is False otherwise

x = 5

x == 5

x == 7

x = 7

x == 7

7 == x

7 = x

# Order of operations matters!
# *, /, % happen first, in the order they appear
1 + 3 * 20 % 7

Operations (boolean types)

# Booleans can be combined using logical ands
# The result of logical and is True if and only if both sides are True
True and False

#Is True==True and False==True?

# Booleans can be combined using logical ors
# The result of logical or is True if either side is True
True or False

#is True==True or False==True?

# You can put operations that result in booleans and combine them
(1 == 1) and (2 == 2)

# Logical negation changes True to False
not True

# and False to True
not False

not (1 == 1)

Operations (string, list)

# Adding strings is called "concatenation"
'Hello' ' '+ 'world!'

# Aside: can you have a 1-element list?
len([27])

# Aside: can you have a 0-element list?
len([])

# Adding list is also called "concatenation"
[0] + [1]

x = [0]
y = [1]
x + y

Errors

# Errors occur when something you do that isn't allowed
# Remember: True is supposed to be capitalized!
true

# Variables must be assigned before being used
print(boaz)

# Once you assign a variable you can use it
boaz = 7
print(boaz)

# Dividing by 0 is undefined and thus an error in Python
1 / 0

Issues to watch out for

Different types of parenthesis (,) .. [,] ... {,}

L = [1,2,3] # list
L[1]

2

(2+3)*4 , 2+3*4

(20, 14)

print("hello")

hello