Python determines when code blocks begin and stop by looking at the space at the beginning of the line. You may encounter the following Indentation errors: 1. Unexpected indent - This line of code has more spaces at the beginning than the one before it, but the one before it does not begin a subblock. In a block, all lines of code must begin with the same string of whitespace. 2. Unindent does not correspond to any of the outer indentation levels - This line of code contains less spaces at the beginning than the previous one, but it also does not match any other block. 3. An indented block was expected - This line of code begins with the same number of spaces as the previous one, yet the previous line was supposed to begin a block (e.g., if/while/for statement, function definition).