Tips for writing efficient Python code

Find the difference of keys between two dictionaries

Suppose two dictionaries A and B. We would like to find the keys in A but not in B.

Bad example:

import time
A = {}
B = {}
for i in range(1000):
	A[i] = i
for i in range(800, 1800):
	B[i] = i
result = []
t = time.clock()
for key in A:
	if (B.has_key(key) != True):
		result.append(key)
elapsed_time = time.clock() - t
print ('elapsed time :' + str(elapsed_time/num_product))
print (result)		

elapsed time :1.58506018256e-06

import time
A = {}
B = {}
for i in range(1000):
	A[i] = i
for i in range(800, 1800):
	B[i] = i
result = []
t = time.clock()
for key in A:
	if (key not in B):
		result.append(key)
elapsed_time = time.clock() - t
print ('elapsed time :' + str(elapsed_time/num_product))
print (result)	

elapsed time :1.06822538939e-06

Good example:

import time
A = {}
B = {}
for i in range(1000):
	A[i] = i
for i in range(800, 1800):
	B[i] = i
result = []
t = time.clock()
result = list(set(A) - set(B))
elapsed_time = time.clock() - t
print ('elapsed time :' + str(elapsed_time/num_product))
print (result)

elapsed time :4.65752280715e-07

Sort and Iterate the Dictionary

Here we use the OrderedDict to sort normal dictionary

Bad example:

import time
import collections
A = {}
for i in range(1000):
	A[i] = i
A = collections.OrderedDict(sorted(A.items()))
#A = dict(A)
t = time.clock()
result = 0 
for key in A:
	result += 1
elapsed_time = time.clock() - t
print ('elapsed time :' + str(elapsed_time/num_product))
print (result)

elapsed time :9.57045813266e-07

Good example:

import time
import collections
A = {}
for i in range(1000):
	A[i] = i
A = collections.OrderedDict(sorted(A.items()))
A = dict(A)
t = time.clock()
result = 0 
for key in A:
	result += 1
elapsed_time = time.clock() - t
print ('elapsed time :' + str(elapsed_time/num_product))
print (result)

elapsed time :4.95800812545e-07