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PYTHON | QUICK REFERENCE GUIDE
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ON THIS PAGE
SECTION 1 | BASIC SYNTAX SECTION 2 | DATA TYPES & OPERATORS SECTION 3 | IF STATEMENTS SECTION 4 | LOOPS SECTION 5 | ARRAYS SECTION 6 | 2D ARRAYS SECTION 7 | FUNCTIONS |
ALSO IN THIS TOPIC
GETTING STARTED VARIABLES AND DATA TYPES OPERATORS SELECTION ITERATION ARRAYS FUNCTIONS AND PROCEDURES FORMATTING DATA ERROR CHECKING OBJECT ORIENTED PROGRAMMING FURTHER PYTHON YOU ARE HERE | PYTHON QUICK REFERENCE |
ELEMENT |
DESCRIPTION |
Variables |
Variables are containers for storing data values. Remember the rules for creating variables. VARIABLE NAMING RULES ✘ Cannot start the name with a number ✘ Cannot contain spaces ✘ Cannot use command words such as print, python, turtle, exit, for, while and many more... VARIABLE NAMING CONVENTIONS ✓Should start with a lowercase letter ✓If more than one word used the first letter uppercase of proceeding words or use _ to join words ✓Names should be meaningful to the content of the variable firstName = "John" age = 25 |
input() |
The input() function allows you to prompt the user for input. user_name = input("Enter your name: ") |
Single Line Comments |
Used to add comments to your code that Python will ignore during execution. # This is a single-line comment |
Multi Line Comments |
Python does not have a specific syntax for multi-line comments, but you can use triple quotes. ''' This is a multi-line comment. Python will ignore this during execution. ''' |
print() |
The print() function outputs text or variables to the console. print("Hello, World!") |
Strings |
Strings are sequences of characters, enclosed in either single or double quotes. greeting = ("Hello") |
Concatenate with + |
Concatenate strings and variables using the + sign joins them together as one value. message = ("Hello " + name) |
Concatenate with , |
Using a comma in the print() function to join strings and variables. print("Hello", name) |
Concatenate with f{} |
Using the f method to format strings allow you to embed expressions inside string literals. message = (f"My name is {name} and I am {age} years old.") |
ELEMENT |
DESCRIPTION |
string |
Strings are sequences of characters, enclosed in either single or double quotes. greeting = ("Hello") age = ("10") #Remember if you put a number in speech-marks Python will treat it as a string/text |
integer - int |
int - this is a integer number (no decimal places) num = (10) |
float |
float - the is a number with decimal places num = (10.55) |
boolean |
Boolean represents one of two values: True or False. is_student = True has_graduated = False |
ELEMENT |
DESCRIPTION |
EXAMPLE |
if |
Used to perform different actions based on different conditions. if: Executes a block of code if the specified condition is true. |
if age > 18: print("You are an adult.") |
elif |
Executes a block of code if the previous conditions were not true, but the current condition is true. |
if age < 13: print("You are a child.") elif age < 18: print("You are a teenager.") |
else |
Executes a block of code if no conditions are true. |
if age < 18: print("You are not an adult.") else: print("You are an adult.") |
indentation |
In Python, indentation is used to define code blocks. Unlike many other programming languages that use braces {} or other symbols to define code blocks, Python uses whitespace (tabs). Purpose: Indentation allows Python to determine which statements belong to a particular code block, such as those inside a loop or a conditional statement. This makes the code more readable and enforces a consistent structure. |
age = int(input("how old are you: ")) if age > 18: print("You are an adult.") name = input("What is your name") #In this example only the print statement is inside the if statement |
ELEMENT |
DESCRIPTION |
EXAMPLE |
for value in |
Iterates over a sequence (like a list, tuple, or string) and executes a block of code for each item in the sequence. |
for fruit in ["apple", "banana"]: print(fruit) |
for num in range |
The range() function returns a sequence of numbers, starting from 0 by default, and increments by 1 (also by default), and stops before a specified number. |
for num in range(5): print(num) # Outputs: 0, 1, 2, 3, 4 |
Specifying Start and Stop |
Generates a sequence of numbers starting from the first specified number up to (but not including) the second specified number. |
for i in range(2, 5): print(i) # Outputs: 2, 3, 4 |
Specifying Step |
Adds a third argument to specify the increment. |
for i in range(0, 10, 2): print(i) # Outputs: 0, 2, 4, 6, 8 |
while |
Executes a block of code as long as the specified condition is true. |
count = 0 while count < 5: print(count) count += 1 |
break |
Used to change the behavior of loops during their execution. break: Exits the loop and continues executing the code after the loop. |
for number in range(10): if number == 5: break print(number) |
continue |
Skips the current iteration of the loop and continues with the next iteration. |
for number in range(5): if number == 2: continue print(number) |
pass |
A null operation; nothing happens when it's executed. It's used as a placeholder. |
for letter in "Python": if letter == "h": pass print(letter) |
DESCRIPTION |
EXAMPLE |
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append() |
Adds an element to the end of the list. |
fruits = ["apple", "banana"] fruits.append("cherry") print(fruits) # Outputs: ['apple', 'banana', 'cherry'] |
remove() |
Removes the first occurrence of the specified value from the list. |
fruits = ["apple", "banana", "cherry"] fruits.remove("banana") print(fruits) # Outputs: ['apple', 'cherry'] |
pop() |
Removes the element at the specified position, or the last element if no index is specified. |
fruits = ["apple", "banana", "cherry"] fruits.pop(1) print(fruits) # Outputs: ['apple', 'cherry'] |
extend() |
Adds elements from another list (or any iterable) to the end of the current list. |
fruits = ["apple", "banana"] fruits.extend(["cherry", "date"]) print(fruits) # Outputs: ['apple', 'banana', 'cherry', 'date'] |
count() |
Returns the number of times the specified value appears in the list. |
numbers = [1, 2, 3, 2, 4, 2] count = numbers.count(2) print(count) # Outputs: 3 |
index() |
Returns the index of the first occurrence of the specified value. |
fruits = ["apple", "banana", "cherry"] idx = fruits.index("banana") print(idx) # Outputs: 1 |
sort() |
Sorts the list in ascending order by default. |
numbers = [3, 1, 4, 2] numbers.sort() print(numbers) # Outputs: [1, 2, 3, 4] |
reverse() |
Reverses the order of the list. |
fruits = ["apple", "banana", "cherry"] fruits.reverse() print(fruits) # Outputs: ['cherry', 'banana', 'apple'] |
copy() |
Returns a copy of the list. |
newList = myList.copy() |
clear() |
Removes all the elements from the list |
listName.clear() |
set() |
Remove duplicates from a list |
myList2 = set(myList1) |
ELEMENT |
DESCRIPTION |
EXAMPLE |
Accessing Elements |
Access elements using row and column indices. |
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] print(matrix[1][2]) # Outputs: 6 |
Appending Rows |
Add a new row to the 2D list. |
matrix = [[1, 2, 3], [4, 5, 6]] matrix.append([7, 8, 9]) print(matrix) # Outputs: [[1, 2, 3], [4, 5, 6], [7, 8, 9]] |
Appending Columns |
Add a new column to the 2D list. |
matrix = [[1, 2], [4, 5], [7, 8]] for row in matrix: row.append(0) # Appending 0 to each row print(matrix) # Outputs: [[1, 2, 0], [4, 5, 0], [7, 8, 0]] |
Removing Rows |
Remove a row from the 2D list. |
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] matrix.pop(1) print(matrix) # Outputs: [[1, 2, 3], [7, 8, 9]] |
Flattening a 2D List |
Convert a 2D list into a 1D list. |
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] flattened = [num for row in matrix for num in row] print(flattened) # Outputs: [1, 2, 3, 4, 5, 6, 7, 8, 9] |
ELEMENT |
DESCRIPTION |
EXAMPLE |
Defining Functions |
Functions are blocks of reusable code. They are defined using the def keyword. |
def greet(name): return f"Hello, {name}!" print(greet("Alice")) # Outputs: Hello, Alice! |
Positional Arguments |
Functions can take arguments (inputs) and return values (outputs). Positional Arguments: Arguments passed in order. |
def add(x, y): return x + y |
Keyword Arguments |
Keyword Arguments are Arguments passed by name. |
def print_info(name, age): print(f"Name: {name}, Age: {age}") print_info(age=30, name="John") |
Default Arguments |
Default Arguments are Arguments with default values. |
def greet(name="Guest"): return f"Hello, {name}!" print(greet()) # Outputs: Hello, Guest! |
Return Values |
Use the return keyword to send a result back |
def square(num): return num * num result = square(4) # result is 16 |
*args |
*args allows you to pass a variable number of positional arguments to a function. Inside the function, args is a tuple containing all passed arguments. |
def add_numbers(*args): return sum(args) print(add_numbers(1, 2, 3, 4)) # Outputs: 10 |
*kwargs |
**kwargs allows you to pass a variable number of keyword arguments to a function. Inside the function, kwargs is a dictionary containing all passed keyword arguments. |
def print_data(**kwargs): for key, value in kwargs.items(): print(f"{key}: {value}") print_data(name="John", age=30, country="USA") # Outputs: # name: John # age: 30 # country: USA |
