Python Basics

The standard file extension for Python source code files.

A valid variable name starts with a letter or underscore, followed by letters, numbers, or underscores (varName).

Multiplication happens before addition, so 3 * 2 = 6, then 2 + 6 = 8.

The # symbol indicates the start of a comment; the interpreter ignores comment lines.

The input() function allows a program to receive text input from the user.

The len() function counts the number of characters in a string, including spaces and special characters. 'Hello' has 5 characters.

The '//' operator performs integer division, it returns the whole number of times one number divides into another. 10 divided by 3 is 3.333, the '//' truncates to 3.

The int() function attempts to convert its argument to a whole number.

The 'def' keyword is used when creating a function in Python.

The 'for' loop iterates through a sequence (e.g., a range of numbers).

Python 3 uses float division by default, so 5 / 2 results in 2.5 (a float).

Tuples are immutable, meaning once created, their elements cannot be modified.

Like any object, a tuple CAN be reassigned with a new tuple with all new values.

In class methods, 'self' refers to the instance of the class, allowing access to instance attributes.

List comprehensions offer a concise way to create lists, improving readability and often performance.

The ** operator performs exponentiation. Thus 2**3 calculates 2 to the power of 3 (2 cubed) which equals 8.

The get() method retrieves the value for a specified key. If the key is missing, it returns a default value (here, "default").

Dictionaries use keys to store values, allowing for very fast lookups; lists require iterating through for searches.

Sets only store unique elements. Adding a duplicate has no effect.

The int() function tries to convert a string to an integer, but only works if the string represents a valid integer. 'abc' cannot be converted to an integer.

Try-except blocks catch runtime errors, allowing the program to continue. Syntax, logical errors are not handled by try-except blocks.

A defined function that is never called consumes memory but has no other effect on the program.

Optimizing algorithms and using built-in functions improve performance; more variables/comments/loops generally decrease performance.

Sets guarantee uniqueness and allow efficient membership tests. Lists do not have this property.

Use a try-except block to catch and handle exceptions, preventing program crashes.

Version control systems track changes and enable collaboration.

List comprehension: concise way to create lists, often improving readability and performance.

Python virtual environments isolate project dependencies, preventing conflicts between different versions of packages.

Tuples are immutable (cannot be modified after creation. Lists, dictionaries, and sets are mutable.

The syntax 'key in my_dict' is used to check whether ‘key’ exists in the keys of the dictionary my_dict. The function my_dict.has_key(x) is used in Python 2 but not in Python 3.

Functions prevent code dupliation and improve readability, reducing redundancy and making code easier to understand/maintain.

Square brackets [] throw a 'KeyError' if the key cannot be found.

List.copy(), list[:] both create a shallow copy of the original list in Python.

In Python, try to use the ‘with‘ statement to handle other program resources like file streams.

The first way is to implement list.sort(reverse=True), and the second way of implementation is sorted(list, reverse=True).

The list comprehension with a condition is one of the methods to remove duplicates from a list while preserving its original order.

An immutable object is defined as an object that cannot be changed after it is created.

The function used in Python to check data type of a variable is the built-in type() function.

The best way to define a function so that it accepts a variable number of arguments is shown by def func(*args):. The ‘*args’ parameter enables a function to accept any number of positional arguments.

Handling exceptions in your code is an excellent way to prevent the program from crashing and provide user feedback.