This Python Exceptions lesson is for a beginner. Read the short notes, run each example, then change one name or number and run it again.
ZeroDivisionError, ValueError, TypeError, KeyError, IndexError, and FileNotFoundError are the exceptions a first project meets.
Catch the specific type. A bare except hides bugs.
Example 1: Start here
Let an unexpected exception crash the program so you can see it.
try: # watch the next lines for an error
print(int("nope")) # int() reads a whole number from the text
except ValueError: # runs when the try block fails
print("not a whole number")
Example 2: Store the idea in a name
Python Exceptions begins with a value you can point at. The name topic holds that text.
topic = "Python Exceptions" # text
print(topic)
Example 3: Check it with if
An if chooses one branch. Change the score and run it again to see the other message.
score = 15 # a whole number
if score >= 80: # run the indented lines only when this is true
print("Pass")
else: # runs when the test above was false
print("Try again")
Example 4: Repeat with a loop
A for loop runs the indented line once per step. The numbers 1, 2, and 3 are printed on their own lines.
for step in range(1, 4): # repeat once per number; range stops before the last
print("Step", step) # a comma prints each value, with a space between
Let an unexpected exception crash the program so you can see it.
