x = [0]
while True: x.extend(x)

dummy = ' '*num_bytes_to_use_up

>>> open('/proc/meminfo').readlines()[1]
'MemFree:         1248940 kBn'
>>> dummy = ' '*1000000000
>>> open('/proc/meminfo').readlines()[1]
'MemFree:          271472 kBn'
>>> del dummy
>>> open('/proc/meminfo').readlines()[1]
'MemFree:         1243464 kBn'