Performance

1. Don’t check if key in list.

• Don’t

l = [1, 2, 3, 4]

# iterates over three elements in the list
if 3 in l:
    print("The number 3 is in the list.")
else:
    print("The number 3 is NOT in the list.")

• Good

use a set or dictionary

s = set([1, 2, 3, 4])

if 3 in s:
    print("The number 3 is in the list.")
else:
    print("The number 3 is NOT in the list.")

2. Use iteritems() to iterate over large dictionary.

• Don’t

d = {i: i * 2 for i in xrange(10000000)}

# Slow and memory hungry.
for key, value in d.items():
    print("{0} = {1}".format(key, value))

• Good

d = {i: i * 2 for i in xrange(10000000)}

# Memory efficient.
for key, value in d.iteritems():
    print("{0} = {1}".format(key, value))

3. String Concatenation.

• Don’t

string in Python are immutable, so using + to do string concatenation will lead to generate a new memory space to store the new string after + operation.

s = ""
for substring in list:
    s += substring

• Good

s = "".join(slist)

# of using f-string