Whitespace between tokens
Except at the beginning of a logical line or in string literals, the whitespace characters space, tab and formfeed can be used interchangeably to separate tokens. Whitespace is needed between two tokens only if their concatenation could otherwise be interpreted as a different token (e.g., ab is one token, but a b is two tokens).
So in this case, 1if is not a valid token, so the whitespace is optional. The 1 is interpreted as an integer literal of which the if is not a part. So if is interpreted separately and recognized as a keyword.
In xif however, an identifier is recognized, so Python is not able to see that you wanted to do x if there.