Common Python Syntax and Runtime Errors with Practical Fixes

SyntaxError: invalid syntax – Often caused by missing or incorrect colons after statements like if , while , or for , unmatched parentheses, or using an assignment operator instead of a comparison. Fix by adding the proper colon, closing brackets, or using == for comparisons.

Syntax Error: non-default argument follows default argument – Occurs when a function defines a parameter with a default value before a parameter without one. Reorder the parameters so that all non‑default arguments precede default arguments.

SyntaxError: invalid character in identifier – Triggered by illegal characters (e.g., @, #, spaces) or identifiers starting with a digit. Use only letters, digits, and underscores, and start with a letter or underscore.

TypeError: can only concatenate str (not “XXX”) to str – Happens when attempting to concatenate a string with a non‑string object. Convert the non‑string value using str() before concatenation.

TypeError: f() takes exactly 2 arguments (1 given) – Raised when a function is called with fewer arguments than required. Supply the missing arguments or adjust the function definition.

TypeError: ‘tuple’ object does not support item assignment – Tuples are immutable; trying to modify an element causes this error. Convert the tuple to a list, modify, then convert back if needed.

ValueError: could not convert string to float: ‘12.2s’ – Occurs when float() receives a non‑numeric string. Ensure the string contains only numeric characters or remove units before conversion.

ValueError: invalid literal for int() with base 10 – Raised when int() receives a string with non‑digit characters or a decimal point. Use float() first if the value may be a float, then cast to int , or validate the string with str.isdigit() .

ValueError: substring not found – Happens when methods like index() or find() cannot locate a substring. Verify the substring exists before searching.

ZeroDivisionError: division by zero – Triggered by dividing by zero. Check the divisor before performing division and handle the case with conditional logic.

AttributeError: ‘module’ object has no attribute … – Caused by misspelling an attribute, using a Python keyword as a filename, or accessing a module via the wrong alias. Correct the spelling, rename the file, or use the proper alias.

AttributeError: ‘Obj’ object has no attribute ‘attr’ – Results from misspelling the attribute name, trying to access a private attribute, or using an object method on the wrong type. Verify the attribute name, respect naming conventions, and call methods on appropriate objects.

FileExistsError: [Errno 17] File exists – Occurs when attempting to create a file that already exists. Check for the file’s existence before creation.

FileNotFoundError: [Errno 2] No such file or directory – Raised when a specified file or directory cannot be found. Verify the path is correct.

IndentationError: expected an indented block – Missing indentation after statements like def , if , for , etc. Add the required indentation.

IndentationError: unexpected indent – Extra or inconsistent indentation. Remove the superfluous spaces or tabs.

IndentationError: unindent does not match any outer indentation level – Mixed indentation styles within the same block. Use a consistent indentation scheme (e.g., 4 spaces).

IndexError: list index out of range – Accessing a list element beyond its length or when the list is empty. Ensure the index is within bounds and the list is non‑empty.

KeyError: ‘age’ – Attempting to retrieve a dictionary key that does not exist. Use an existing key or check with in before access.

ModuleNotFoundError: No module named ‘pymysql’ – The module is not installed, misspelled, or not available in the current environment. Install the module, correct the name, or activate the appropriate virtual environment.

NameError: name ‘test’ is not defined – Refers to an undefined variable or a variable out of scope. Define the variable before use or adjust its scope.

RecursionError: maximum recursion depth exceeded – Caused by infinite or excessively deep recursion. Limit recursion depth or rewrite the algorithm iteratively.

Timeout error [WinError 10060] – Network or database connection timed out. Verify connection parameters, URLs, and server availability.