Also, the del statement seems to be a little bit faster than assigning None (similar to Java's style assigning null to a variable to free its memory ...).
To compare:
import time, math
def measure_del():
start = time.time()
for i in range(0,int(math.pow(10,8))):
a = "123"
del a # <--- !!!
end = time.time()
print(end-start)
def measure_none():
start = time.time()
for i in range(0,int(math.pow(10,8))):
a = "123"
a = None # <--- !!!
end = time.time()
print(end-start)
results in (running in idle3.4):
>>> measure_del()
3.9930295944213867
>>> measure_del()
3.7402305603027344
>>> measure_del()
3.8423104286193848
>>> measure_del()
3.753770351409912
>>> measure_del()
3.7772741317749023
>>> measure_del()
3.815058946609497
>>> measure_none()
4.052351236343384
>>> measure_none()
4.130320072174072
>>> measure_none()
4.082390069961548
>>> measure_none()
4.100180625915527
>>> measure_none()
4.071730375289917
>>> measure_none()
4.136169672012329