Comments
Contents
Variables and Types#
coolvar = 7 # declaration
coolvar # almost the same as print(myvar)
7
print(7, type(7)) # integer
print(float(7), type(7.0)) # float
7 <class 'int'>
7.0 <class 'float'>
# ALL these are strings
print("Let's go", type("Let's go")) # you can also escape \' when in single quotes
print('"To be or not to be?"', type("'To be or not to be?'"))
a = """This is a multiline
string"""
print(a, type(a))
Let's go <class 'str'>
"To be or not to be?" <class 'str'>
This is a multiline
string <class 'str'>
Operators#
a = 73
b = 42
# addition
print('a + b =', a + b)
# subtraction
print('a - b =', a - b)
# multiplication
print('a * b =', a * b)
# classic division - returns a float
print('a / b =', a / b)
# floor division - discards the fractional part
print('a // b =', a // b)
# remainder of the division
print('a % b =', a % b)
# power (a^2)
print('a ** 2 =', a ** 2)
a + b = 115
a - b = 31
a * b = 3066
a / b = 1.7380952380952381
a // b = 1
a % b = 31
a ** 2 = 5329
print(2 < 5)
print(4 > 10)
print(3 >= 3)
print(5 == 6)
print(6 != 9)
True
False
True
False
True
Implicit Type Conversion - only for some types#
num_int = 123 # integer type
num_flo = 1.23 # float type
num_int + num_flo
124.23
num_int = 123 # int type
num_str = "456" # str type
num_int+num_str
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
Input In [8], in <cell line: 4>()
1 num_int = 123 # int type
2 num_str = "456" # str type
----> 4 num_int+num_str
TypeError: unsupported operand type(s) for +: 'int' and 'str'
str(num_int) + num_str
Data Structures#
my_list = [] # empty list
my_list = [1, 2, 3] # list of integers
my_list = [1, "Hello", 3.4] # list with mixed data types
print(my_list[0]) # Accessing first element
print(my_list[:])
print(my_list[0:2])
print(my_list[-3:-1])
print(my_list[1:])
print(my_list[::2])
language = ("French", "German", "English", "Polish")
str = 'this is a string'
# set of integers
my_set = set()
my_set = {1, 2, 3}
print(my_set)
# set of mixed datatypes
my_set = {1.0, "Hello", (1, 2, 3)}
print(my_set)
# set of integers
my_set = {1, 2, 3}
my_set.add(4)
print(my_set) # Output: {1, 2, 3, 4}
my_set.add(2)
print(my_set) # Output: {1, 2, 3, 4}
my_set.update([3, 4, 5])
print(my_set) # Output: {1, 2, 3, 4, 5}
my_set.remove(4)
print(my_set) # Output: {1, 2, 3, 5}
# empty dictionary
my_dict = {}
# dictionary with integer keys
my_dict = {1: 'apple', 2: 'ball'}
# dictionary with mixed keys
my_dict = {'name': 'John', 1: [2, 4, 3]}
person = {'name':'Jack', 'age': 26, 'salary': 4534.2}
print(person['age'])
Python Control Flow#
num = -1
if num > 0:
print("Positive number")
elif num == 0:
print("Zero")
else:
print("Negative number")
if False:
print("I am inside the body of if.")
print("I am also inside the body of if.")
print("I am outside the body of if")
n = 100
# initialize sum and counter
sum = 0
i = 1
while i <= n:
sum = sum + i
i = i+1 # update counter
print("The sum is", sum)
numbers = [6, 5, 3, 8, 4, 2]
sum = 0
# iterate over the list
for val in numbers:
sum = sum+val
print("The sum is", sum) # Output: The sum is 28
Functions#
def print_lines():
print("I am line1.")
print("I am line2.")
# function call
print_lines()
def add_numbers(a, b):
sum = a + b
return sum
result = add_numbers(4, 5)
print(result)
def greet(name, msg = "Good morning!"):
"""
This function greets to
the person with the
provided message.
If message is not provided,
it defaults to "Good
morning!"
"""
print("Hello",name + ', ' + msg)
greet("Kate")
greet("Bruce","How do you do?")
def greet(*names):
"""This function greets all
the person in the names tuple."""
# names is a tuple with arguments
for name in names:
print("Hello",name)
greet("Monica","Luke","Steve","John")
Python OOP#
class ComplexNumber:
def __init__(self,r = 0,i = 0): # constructor
self.real = r
self.imag = i
def getData(self):
print("{0}+{1}j".format(self.real,self.imag))
c1 = ComplexNumber(2,3) # Create a new ComplexNumber object
c1.getData()
c2 = ComplexNumber() # Create a new ComplexNumber object
c2.getData()
List Comprehension vs For Loop in Python#
[expression for item in list]
h_letters = []
for letter in 'human':
h_letters.append(letter)
print(h_letters)
h_letters = [letter for letter in 'human']
print( h_letters)
number_list = [ x for x in range(20) if x % 2 == 0]
print(number_list)
matrix = [[1, 2], [3,4], [5,6], [7,8]]
transpose = [[row[i] for row in matrix] for i in range(2)]
print (transpose)
Miscelanneous#
list(range(1, 10))
Comments#