Python Basics, Tips & Tricks

Exception Handling

try-except-else(optional)-finally(optional)

try:

    # code

except SomeError1:

    # handle error

except SomeError2:

    # handle error

except Exception as e:

    print(f"An error occurred: {e}")

else:

    # runs if no error

finally:

    # always runs; useful for cleanup, closing resorces

Raising Exception

def set_age(age):

    if age < 0:

        raise ValueError("Age cannot be negative!")

    return age

False in Conditionals

• In condition check, the following = False

  • 0

  • "" (empty string)

  • [], {}, set()

  • None

  • False

Example:

if my_list:

    print("Not empty!")

Swapping Variables Without a Temp

• Swap values in one line:

a, b = b, a

_ as a Throwaway Variable

• If you don't care about a variable:

for _ in range(5):

    print("Hello")

The "Walrus Operator" (Python 3.8+)

• Assign inside expressions:

if (n := len("hello")) > 3:

    print(n)

The special variable __name__

• When Python runs a file, it assigns the special variable __name__.

• If the file is being run directly (like python myfile.py), then:

  • __name__ == "__main__"

• If the file is being imported into another file (like import myfile), then:

  • __name__ == "myfile"

Python File as a Script vs Module:

• A script (something you run directly).

• A module (something you import into other files).

Example: myfile.py

def hello():

    print("Hello!")

# bash: python myfile.py → runs hello()

# import myfile → doesn't run hello()

if __name__ == "__main__":

    hello()