15 Common Python Errors for Beginners and How to Fix Them

How to read a traceback

Every Python error prints a traceback. Read the last line first: it names the error type and gives a message. Then look at the line above it for the file and line number. The lines further up show the chain of function calls that led there. In the Coding Python app the console highlights the error type, so this habit transfers directly.

Syntax and indentation errors

1. SyntaxError: expected ':'

if x > 3
    print(x)

Fix: every if, elif, else, for, while, def, class, try and with line ends with a colon.

2. SyntaxError: '(' was never closed

print("total:", sum([1, 2, 3])

Fix: count your brackets. Modern Python (3.10+) points at the unclosed one. Editors with bracket matching, including the app's, help.

3. SyntaxError: invalid syntax — using = instead of ==

if score = 100:
    print("perfect")

Fix: = assigns, == compares. Use if score == 100:.

4. IndentationError: expected an indented block

for i in range(3):
print(i)

Fix: the body of a block must be indented (four spaces). unindent does not match any outer indentation level means you mixed tabs and spaces or lined up inconsistently.

5. SyntaxError: Missing parentheses in call to 'print'

print "hello"

Fix: that is Python 2 syntax. Write print("hello"). The tutorial you copied it from is out of date.

Name and attribute errors

6. NameError: name 'x' is not defined

total = 10
print(totl)

Fix: usually a typo, or you used the variable before assigning it, or it was assigned inside a function and you are outside. Check spelling and order.

7. AttributeError: 'list' object has no attribute 'push'

items = []
items.push(1)

Fix: the method does not exist on that type. Lists use append. Run dir(items) or help(list) to see what is available. If the message says 'NoneType' object has no attribute…, a function returned None — commonly lst = lst.sort().

8. ModuleNotFoundError: No module named 'requests'

Fix: the package is not installed (pip install requests) or the name is misspelled. In the Coding Python app only the standard library is available — check the standard library lesson for alternatives.

Type and value errors

9. TypeError: can only concatenate str (not "int") to str

age = 30
print("Age: " + age)

Fix: convert or format: print(f"Age: {age}") or "Age: " + str(age). — Strings

10. TypeError: 'int' object is not iterable

for i in 5:
    print(i)

Fix: loop over range(5). The same message with 'NoneType' means you are looping over a function result that was None.

11. TypeError: greet() missing 1 required positional argument: 'name'

Fix: the function expects an argument you did not pass. Check the definition; give the parameter a default if it is optional. — Functions

12. ValueError: invalid literal for int() with base 10: 'abc'

n = int(input("Number: "))    # user typed abc

Fix: wrap in try/except ValueError and ask again. — Exceptions

Index and key errors

13. IndexError: list index out of range

nums = [1, 2, 3]
print(nums[3])

Fix: indexes start at 0, so the last item is nums[len(nums) - 1] or nums[-1]. Loops that use range(len(x) + 1) cause this too.

14. KeyError: 'email'

user = {"name": "Ada"}
print(user["email"])

Fix: use user.get("email", "n/a") or check if "email" in user. — Dictionaries

15. ZeroDivisionError: division by zero

average = total / count     # count is 0

Fix: guard it: average = total / count if count else 0.

Reproduce these errors safely in the app — the Coding Python app runs real Python 3 on your phone, with examples, quizzes and challenges built in.

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Bonus: bugs that raise no error

• Infinite loop — the while condition never becomes false. Stop the program and make sure something inside the loop changes it.
• Integer division surprise — 5 / 2 is 2.5, 5 // 2 is 2.
• Float comparison — 0.1 + 0.2 == 0.3 is False. Compare with a tolerance or use round().
• Shadowing a built-in — naming a variable list, str or sum breaks the built-in for the rest of the program.
• Mutable default argument — def f(x=[]) shares one list across calls.

Every one of these is easier to spot with fast feedback, which is a good argument for running code often while you write it.

Frequently asked questions