Common error messages
This page contains information about the most common error messages you may come across when completing the programming exercises on this course.
Make sure your program doesn't print any extra whitespace, such as space characters. Notice that the default behaviour of the
print("Hello","World!") # This prints out: Hello World!
This error message usually appears when there is a typo in your code which the Python interpreter finds hard to classify more specifically. For example, there may be a colon character missing from the end of an
if statement, or a keyword, such as
while, may have been misspelled. The only way to fix this problem is to inspect the line indicated in the error message.
number1 = 1
number1 = 2
if number1 < number2 # ':' missing
print('number2 is greater')
If the line indicated in the error message looks correct, the error may often be one line above or below the line indicated, so check around the issue, too.
NB: The programming exercises in the early parts of this course use a framework called Skulpt to run Python code in the browser. Skulpt is quite limited compared to a regular Python interpreter, and thus the error messages printed out are often less informative. For example, the
bad input on line error message may refer to many different programming errors, and it is difficult to find out the true cause of the error just based on this message.
Your code is indented incorrectly at the line indicated in the error message. For example, all lines within an
if block must be indented the same. To fix this error, indent all lines within a block of code with the exact same amount of whitespace.
The following code would cause this error:
You are trying to refer to a variable or object which does not exist at that specific point in your program. It may be that the variable has not yet been assigned a value, or there is a typo in the variable name. It may also be the case that you have defined a variable inside a function, and are trying to refer to that same variable outside the function.
person = input('Please type in your name: ')
input('Please type in your age: ')
print("Hi", pearson) # error: person was typed pearson
print("You are", age, "years old") # error: the variable age has not been defined
You may be trying to add an integer and a string together, without first converting the string into an integer value. Strings can be converted into integers with the
int() function. A similar error message may appear if you try to perform other arithmetic operations, such as division or subtraction, on strings.
It may also be the case that you are trying to create a new string by combining a string and an integer. You should first convert the integer into a string with the
my_age = input("Please type in your age: ")
my_name = input("Please type in your name: ")
print(my_age//2) # error: the variable my_age has not been converted into an integer