In Python, there are two kinds of errors: syntax errors and runtime errors.

Syntax errors occur when you write code that Python does not understand. For example:

if = 5

This example is incorrect because if cannot be used as a variable. If you try to run this program, you will get an error that looks something like this:

  File "C:\Documents and Settings\Administrator\My Documents\test.py", line 1
    if = 5
       ^
SyntaxError: invalid syntax

When Python detects a syntax error, it tries to make a best guess as to where the problem is located.

Runtime errors are trickier, as they cannot be detected until your program is actually running. For example, here is a simple program that generates a runtime error:

totalcost = 4000
days = 0
cost = totalcost / days
print "Cost per day is", cost

This code does not contain any syntax errors, as each statement is perfectly legal Python. But, when you try to run the program, it generates a runtime error when it tries to divide 4000 by 0:

Traceback (most recent call last):
  File "C:\Documents and Settings\Administrator\My Documents\test.py", line 3, in ?
    cost = totalcost / days
ZeroDivisionError: integer division or modulo by zero

As you can see, the program stops running when the runtime error is detected. This might not be the outcome you want: if your program is processing a large amount of data, you might not want it to halt whenever it detects a runtime error. Instead, you would likely want the program to deal gracefully with the error and continue running.