Answers

F2.1 Blocks and indentation

Decisions and loops · GCSE · OCR J277 2.2.1, AQA 8525 3.2.2, Edexcel 1CP2 6.2.1 · about 10 min

What this lesson is about

How Python groups lines: the colon and the indent.

• A block is a group of lines
• The colon and the indent go together
• How much to indent
• Where a block ends
• Blocks inside blocks
• Why Python does it this way

Questions 7 marks in all

1. [1 mark]What does this program print?

   if True:
       print("one")
       print("two")
   print("three")

   Answer:

   one
   two
   three

   The two indented lines are the block. The unindented line is not part of it and runs anyway.

2. [1 mark]What must a line that starts a block end with?

   1. AA colon :
   2. BA semicolon ;
   3. CA full stop
   4. DBrackets ()
   Answer: A. The colon says a block follows, and the next lines must be indented.

3. [1 mark]What does Python say about a line indented for no reason, with no : line above it?

   1. AIndentationError: unexpected indent
   2. BNothing, it runs normally
   3. CNameError
   4. DIt skips the line
   Answer: A. Indentation must belong to a block. Indentation with no block is an error.

4. [1 mark]Two lines in the same block are indented by four spaces and three spaces. What happens?

   1. AIndentationError: lines in one block must line up exactly
   2. BBoth run
   3. COnly the first runs
   4. DPython fixes it
   Answer: A. What Python cares about is that every line in the same block has the same indentation.

5. [1 mark]How many spaces is the usual indent for a block inside a block?

   Answer: 8. Four spaces for each level: a block inside a block is eight spaces in.

6. [1 mark]Where does a block end?

   1. AAt the first line that is indented less
   2. BAt the next blank line
   3. CAt the next print
   4. DAt the end of the program, always
   Answer: A. The first line indented less than the block is outside it.

7. [1 mark]In OCR's Exam Reference Language, which word closes an if block?

   1. Aendif
   2. Bend
   3. Cfi
   4. DNothing: indentation is enough
   Answer: A. The Reference Language closes blocks with words: endif, endwhile, next. Python uses indentation alone.

The task: fix the indentation

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

if True:
print("inside the block")
# the LED: green
led("green")
    print("after the block")

from bugbot import *
connect()
if True:
    print('inside the block')
    led('green')
print('after the block')