Python Basics For Beginners

1. Data Types

Python is an extremely popular language which is primarily used in Data Science, Web Development and Bioscience. The syntax is known to be easy to read and learn and has a lot of similarities to the English Language.

• New lines are used to indicate the end of a conditional statement, loop or function
• Indentation is used to indicate scope (e.g. a piece of code will only run within a function)
• Variables are storage containers for different types of data

example_variable = 12 # Integer -> int
example_variable = "Hello World" # String -> str
example_variable = 12.4 # Float -> float
example_variable = complex(2, -3) # Complex -> complex
example_variable = [1, 2, 3] # List -> list
example_variable = (1, 2, 3) # Tuple -> tuple
example_variable = range(5) # Range -> range
example_variable = {"element1" : 1} # Dictionary -> dict
example_variable = True # Boolean -> bool

2. Printing

Prints a message onto the screen

print("Hello World")

3. Strings

A sequence of characters

Creating

example_string = "Hello World"
print(example_string) 
# OUTPUT: Hello World

Concatenation

first_string = "Hello "
second_string = "World"
third_string = first_string + second_string
print(third_string) 
# OUTPUT: Hello World

Slicing

example_string = "Hello World"
print(example_string[0:5]) 
# OUTPUT: Hello
# Slice using [firstIndex : secondIndex + 1]
# ∴ [0:5] is the first 5 characters (0th to 4th index)

Substitution

example_string = "Hello World"
print("My string is", example_string)
# OUTPUT: My string is Hello World

Special Methods

example_string = "Hello World"
print(example_string.upper())
# OUTPUT: HELLO WORLD
print(example_string.lower())
# OUTPUT: hello world
print(type(example_string))
# OUTPUT: <type 'str'>

4. Lists

A mutable data structure which contains an ordered sequence of elements

Creating

example_list = ["element1", "element2", "element3"]
print(example_string) 
# OUTPUT: ["element1", "element2", "element3"]

Adding

example_list = ["element1", "element2"]
example_list2 = ["element3", "element4"]
example_list3 = example_list + example_list2
print(example_string3) 
# OUTPUT: ["element1", "element2", "element3", "element4"]

Sorting

example_list = [34, 4, 8, 1, 49, 310, 15]
example_list.sort()
print(example_list)
# OUTPUT: [1, 4, 8, 15, 34, 49, 310]

Slicing

example_list = [34, 4, 8, 1, 49, 310, 15]
print(example_list[1:4])
# OUTPUT: [4, 8, 1]

Converting to Tuples

example_list = [34, 4, 8, 1, 49, 310, 15]
print(tuple(example_list))
# OUTPUT: (34, 4, 8, 1, 49, 310, 15)

5. Tuples

An immutable data structure which contains an ordered sequence of elements

Creating

example_tuple = (1, 2, 3)
print(example_tuple) 
# OUTPUT: (1, 2, 3)

Slicing

example_tuple = (1, 2, 3, 4, 5, 6)
print(example_tuple[2:4]) 
# OUTPUT: (3, 4)

Converting to Lists

example_list = (34, 4, 8, 1, 49, 310, 15)
print(list(example_list))
# OUTPUT:[34, 4, 8, 1, 49, 310, 15]

6. Dictionaries

A data structure in the form of an associate array (i.e. key-value pairs)

Creating

example_dict = {"element1":1, "element2":2}
print(example_dict) 
# OUTPUT: {"element1":1, "element2":2}

Accessing

example_dict = {"element1":1, "element2":2}
print(example_dict["element2"]) 
# OUTPUT: 2

Key Existence

example_dict = {"element1":1, "element2":2}
print("element1" in example_dict) 
# OUTPUT: True

Keys

example_dict = {"element1":1, "element2":2}
print(example_dict.keys()) 
# OUTPUT: dict_keys(['element1', 'element2'])

7. Conditional Statements

Helps perform different computation based on specific criteria

If-Elif-Else

example_number = 20
if example_number > 10:
  print("Greater than 10")
elif example_number < 10:
  print("Less than 10)
else:
  print("Equal to 10)
# OUTPUT: Greater than 10
example_list = [1, 2, 3, 4]
number = 5
if number not in example_list:
  print(number, "is not in the list")
# OUTPUT: 5 is not in the list

8. Loops

Helps iterate over a sequence (e.g. string, list, tuple, dictionary) and execute code on each individual element

For

for current_value in range(1, 6):  
  print(current_value)
# OUTPUT: 1
# OUTPUT: 2
# OUTPUT: 3
# OUTPUT: 4
# OUTPUT: 5

While

current_value = 1 
while current_value <= 5:  
  print(current_value)
  current_value += 1
# OUTPUT: 1
# OUTPUT: 2
# OUTPUT: 3
# OUTPUT: 4
# OUTPUT: 5

9. User Input

Helps read and store input from the keyboard

age = input("How old are you? ")
print(age)
# OUTPUT: 12

10. Functions

A block of modular, reusable code that tends to perform a single action

Declaring

def example_function():
  print("Hello World!")
example_function()
# OUTPUT: Hello World!

Passing in arguments

def example_function(num1, num2):
  print(num1 + num2)
example_function(2, 5)
# OUTPUT: 7

Return values

def example_function(num1, num2):
  return num1 + num2
returned_number = example_function(2, 5)
print(returned_number)
# OUTPUT: 7