TypeError

TypeError is raised when an operation or function is applied to an object of inappropriate type. This is different from ValueError, which deals with the right type but wrong value.

Common causes

• Concatenating incompatible types: "age: " + 25
• Calling a non-callable object
• Wrong number of arguments to a function
• Using unsupported operand types (e.g., str - int)
• Iterating over a non-iterable (e.g., for x in None)

How to fix it

• Convert types explicitly: str(25), int("10")
• Use f-strings for string formatting: f"age: {25}"
• Check callable with callable() before calling
• Verify argument count matches function signature
• Use isinstance() to check types before operations

Example

# Error example
result = "age: " + 25
# TypeError: can only concatenate str (not "int") to str

len(42)
# TypeError: object of type 'int' has no len()

# Fix with f-string
result = f"age: {25}"  # "age: 25"

# Fix with str()
result = "age: " + str(25)  # "age: 25"

# Fix with type check
def process(items):
    if not isinstance(items, (list, tuple)):
        items = [items]
    for item in items:
        print(item)

Related errors