- Indentation: the first line is not indented correctly, it won't compile as-is. Therethere is an extra tab or spaces before
def listsmash(listu):.
- Code formatting: follow PEP 8 to format the code. You can use pep8online or just use the auto-formatting feature of many IDEs.
- Bug: the output should be
apples, bananas, tofu, and cats but the code outputs apples,bananas,tofu,and cats. There should be a space after the comma.
- Edge case: if the input list contains only
apples the code outputs and apples. This is an edge case to handle, probably at the beginning of the method.
- Performance: there is no much to worry about performances, as it runs linearly to the input size. However, the first if condition is executed everytime:
for x in range(len(listu)):
if x == len(listu) -1 :
y+= 'and '+ str(listu[x])
else:
y+= str(listu[x]) + ','
Limit the number of iterations to len(listy) - 1 and add the last element outside the for-loop:
def listsmash(listu):
y = ''
for x in range(len(listu) - 1):
y += str(listu[x]) + ', '
y += 'and ' + str(listu[-1])
return y
- Use string.join: string.join is a handy function in this case:
def listsmash(listu):
y = ', '.join(str(value) for value in listu[:-1])
return y + ', and ' + str(listu[-1])
JoinsIt joins all elements of listu (except the last one) of listu with , and addthen we can append the last element at the end. Additionally, the function .join() is faster than +=.
- Naming: I am not sure what
listu means, maybe you can consider a better name like items following from the problem description.
Runtime for 1 million items:
Original: 4.321 s
Improved: 0.418 s
Full code:
from random import randint
from time import perf_counter
def original(listu):
y = ''
for x in range(len(listu)):
if x == len(listu) - 1:
y += 'and ' + str(listu[x])
else:
y += str(listu[x]) + ', '
return y
def improved(items):
result = ', '.join(str(item) for item in items[:-1])
return result + ', and ' + str(items[-1])
# Correctness
items = ['apples', 'bananas', 'tofu']
assert original(items) == improved(items)
# Benchmark
n = 1_000_000
items = [randint(0, n) for _ in range(n)]
t0 = perf_counter()
original(items)
total_time = perf_counter() - t0
print(f'Original: {round(total_time, 3)} s')
t0 = perf_counter()
improved(items)
total_time = perf_counter() - t0
print(f'Improved: {round(total_time, 3)} s')
