Python Basics for GCSE Success

The print function in Python is used to display output on the screen. You can pass any string or variable to it, and it will print that value.

A variable in Python is defined by assigning a value to a name using the equals sign. For example, 'a = 5' defines a variable 'a' with the value 5.

Concatenation in Python refers to the process of joining two or more strings together using the plus sign (+). If you want to concatenate a string with an integer, you need to convert the integer to a string first using str().

You can get user input in Python using the input() function. You can prompt the user with a message, and the input will be stored in a variable. For example, 'a = input("Enter a number:")' will store the user's input in variable 'a'.

The main data types in Python include:

1. Integer - whole numbers
2. Float - decimal numbers
3. String - text enclosed in quotes
4. Boolean - True or False values

A loop is a programming construct that allows you to repeat a block of code multiple times. It is used for iteration, which means executing a set of instructions repeatedly until a certain condition is met.

A for loop is a count-controlled loop that iterates over a sequence. It is structured as follows:

1. Use the syntax: for i in range(start, end):
2. The start is optional and defaults to 0.
3. The end is exclusive, meaning it does not include the end value.
4. Indent the code block to execute within the loop.

For example, for i in range(10): will iterate from 0 to 9, printing each number.

You can modify the step size in a for loop by adding a third argument in the range() function:

• Syntax: for i in range(start, end, step):
• For example, for i in range(0, 10, 3): will iterate through 0, 3, 6, and 9.
• You can also use negative values to count backwards, e.g., for i in range(10, 0, -1): will iterate from 10 to 1.

The main differences between a for loop and a while loop are:

To increment a variable in a while loop, you can use:

• x = x + 1 or the shorthand x += 1.

This ensures that the loop progresses towards the exit condition. For example:

x = 0
while x < 10:
    print(x)
    x += 1

Branching or selection in programming refers to making decisions based on conditions, typically implemented using if statements. The basic structure is:

if condition:
    # code to execute if condition is true
elif another_condition:
    # code to execute if another_condition is true
else:
    # code to execute if none of the conditions are true

You can use an if statement to compare the user input with a specific value using double equals (==). For example:

if name == 'a':
    print('invalid')
else:
    print('valid')

The elif statement allows you to check multiple conditions in a sequence. If the first if condition is false, it checks the elif condition. For example:

if name == 'a':
    print('invalid')
elif name == 'b':
    print('valid')
else:
    print('try again')

You can iterate through an array using a for loop combined with the range function. Use the len() function to determine the length of the array. For example:

for i in range(len(a)):
    print(a[i])

In Python, arrays are immutable, meaning once you set their length, you cannot change it. You cannot add or remove elements from an array after it has been created. However, you can change the value of an element at a specific index. For example:

a[2] = 5  # Changes the third element to 5

A function is a block of reusable code that performs a specific task. It can take parameters (inputs) and return a value. Functions are defined using the def keyword. For example:

def area(x, y):
    return x * y

To call a function with parameters, you simply use the function name followed by parentheses containing the arguments. For example:

result = area(5, 10)
print(result)  # Outputs 50

Functions allow for reusability of code, enabling programmers to avoid copying and pasting code multiple times. This promotes the use of reusable components, which is beneficial for maintaining and organizing code.

Printing a value outputs it to the console but does not store it for further use. Returning a value allows it to be stored in a variable, enabling further manipulation or use in the program. For example, if a function returns an area, it can be stored in a variable like Zed and printed later.

Strings can be accessed using indexing just like arrays. For example, if 'subject' is a string, 'subject[1]' will return the second character. Additionally, the length of a string can be determined, and slicing can be used to extract substrings, similar to how it is done with arrays.

Slicing allows you to extract a portion of a string or an array by specifying a start and an end index. The end index is exclusive, meaning it does not include the character or element at that index. For example, 'subject[1:3]' would return characters from index 1 to 2.

When slicing an array, you can specify a range of indices to retrieve elements. For example, if 'a' is an array defined as [1, 2, 3, 4, 5], accessing 'a[1:3]' would return [2, 3], which are the elements at index 1 and 2.