Python - SyntaxError and IndentationError

I know that python is an interpreter language and it means that it interprets the code at run time, so why is that code gives me IndentationError?

def function(x):
    if x:

Does it check all the code before running it?

In Python, functions are objects.

You get an error immediately because the Python interpreter wasn't able to construct a function object from your function definition due to improper syntax. In this case not having an indented block after your if statement.

https://docs.python.org/2/tutorial/controlflow.html#defining-functions

Creating a function instance happens before calling a function.

>>> def errorOnCall(x):
...     return x / 0
... 
>>> print errorOnCall
<function errorOnCall at 0x7f249aaef578>

Function object created due to no syntax error, but the function will raise an error when we invoke it.

>>> errorOnCall(42)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in errorOnCall
ZeroDivisionError: integer division or modulo by zero

Now an error is thrown as soon as we invoke this function.

>>> def errorOnDefinition(x):
...     if x:
... 
  File "<stdin>", line 3

    ^
IndentationError: expected an indented block

This error is thrown when we finish defining our function, but before we invoke it. The interpreter wasn't able to create a function instance from this invalid definition.