# a list of approximated pi values rounded off using list comprehension
# is supposed to give:
# ['3.1', '3.14', '3.142', '3.1416', '3.14159']
# but gives:
# ['3.1000000000000001', '3.1400000000000001', '3.1419999999999999',
#  '3.1415999999999999', '3.1415899999999999']
piList = [repr(round(355/113.0, k)) for k in range(1,6)]
print piList
# this however gives the right result = 3.14159
print round(355/113.0, 5)

list comprehension:
 
result = [expression for item1 in sequence1 [if condition1] 
         [for item2 in sequence2 ... for itemN in sequenceN]
         ]

is equivalent to: 

result = []
for item1 in sequence1:    
  for item2 in sequence2:
    ...
    for itemN in sequenceN:
      if (condition1) and further conditions:
        result.append(expression)