old_contents: # ... integers
  1
  +1
  -1
  a + 2
  3*a + 1
  3*(4+a) + 1
  3/(4+a) + 1
  # ...
  
  # ... floats
  1.
  +1.
  -1.
  a + 2.
  3.*a + 1.
  3.*(4.+a) + 1.
  3./(4.+a) + 1.
  # ...
  
  # ... booleans
  True
  False
  not a
  a and b
  a or b
  # ...
  
  # ... relationals
  a == b
  a != b
  a < b
  a > b
  a <= b
  a >= b
  # ...
  
new_contents: # coding: utf-8
  
  
  1
  +1
  -1
  a + 2
  3*a + 1
  3*(4+a) + 1
  3/(4+a) + 1
  
  
  1.
  +1.
  -1.
  a + 2.
  3.*a + 1.
  3.*(4.+a) + 1.
  3./(4.+a) + 1.
  
  True
  False
  not a
  a and b
  a or b
  
  a == b
  a != b
  a < b
  a > b
  a <= b
  a >= b
  
subject: Update expressions.py