最近在寫一些題目練練手，發現個有趣的東西
題目是這樣的：
You are given a string and you have to find its first word.
- The input string consists of only English letters and spaces.
- There aren’t any spaces at the beginning and the end of the string.
Input: A string (str).
Output: A string (str).
Examples:
assert first_word("Hello world") == "Hello"
assert first_word("a word") == "a"
assert first_word("greeting from CheckiO Planet") == "greeting"
assert first_word("hi") == "hi"
How it is used: The first word is a command in a command line.
Precondition: The text can contain a-z, A-Z and spaces.
我馬上想到，這還不簡單，用 split 之後取第一個值 return 不就好了，所以給出以下程式碼：
def first_word(text: str) -> str:
return text.split(" ")[0]
過是過了，但往下一滑，發現了有趣的東西
def first_word(text):
index = text.find(" ")
return text[:index] if index != -1 else text
"""
It's worth to look at the performance of different methods under the same predefined conditions.
Let's check runtime of the 4 methods (10000 executions for each) defined below for the next 4 cases:
-a short str which contains space chars: "asdf we"*10;
-a short str which doesn't contain space chars: "asdfawe"*10;
-a long str which contains space chars: "asdf we"*100000;
-a long str which doesn't contain space chars: "asdf we"*100000.
############################################################################################################
from timeit import timeit as t
def first_word_1(text):
return text.split(" ")[0]
print(t('first_word_1(x)', setup='x = "asdf we"*10', number=10000, globals=globals())) # ~11.7 ms
print(t('first_word_1(x)', setup='x = "asdfawe"*10', number=10000, globals=globals())) # ~6.1 ms
print(t('first_word_1(x)', setup='x = "asdf we"*100000', number=10000, globals=globals())) # ~90928.2 ms
print(t('first_word_1(x)', setup='x = "asdfawe"*100000', number=10000, globals=globals())) # ~5562.9 ms
def first_word_2(text):
index = text.find(" ")
return text[:index] if index != -1 else text
print(t('first_word_2(x)', setup='x = "asdf we"*10', number=10000, globals=globals())) # ~6.3 ms
print(t('first_word_2(x)', setup='x = "asdfawe"*10', number=10000, globals=globals())) # ~4.7 ms
print(t('first_word_2(x)', setup='x = "asdf we"*100000', number=10000, globals=globals())) # ~7.0 ms
print(t('first_word_2(x)', setup='x = "asdfawe"*100000', number=10000, globals=globals())) # ~2108.4 ms
def first_word_3(text):
try:
index = text.index(" ")
return text[:index]
except ValueError:
return text
print(t('first_word_3(x)', setup='x = "asdf we"*10', number=10000, globals=globals())) # ~5.8 ms
print(t('first_word_3(x)', setup='x = "asdfawe"*10', number=10000, globals=globals())) # ~8.5 ms
print(t('first_word_3(x)', setup='x = "asdf we"*100000', number=10000, globals=globals())) # ~5.8 ms
print(t('first_word_3(x)', setup='x = "asdfawe"*100000', number=10000, globals=globals())) # ~2005.8 ms
def first_word_4(text):
index = -1
for pos, letter in enumerate(text):
if letter == " ":
index = pos
break
return text[:index] if index != -1 else text
print(t('first_word_4(x)', setup='x = "asdf we"*10', number=10000, globals=globals())) # ~13.1 ms
print(t('first_word_4(x)', setup='x = "asdfawe"*10', number=10000, globals=globals())) # ~71.1 ms
print(t('first_word_4(x)', setup='x = "asdf we"*100000', number=10000, globals=globals())) # ~13.1 ms
print(t('first_word_4(x)', setup='x = "asdfawe"*100000', number=10000, globals=globals())) # ~788793.7 ms
############################################################################################################
So what conclusions can be made from all of this?
1.Since every string is an instance of the string class, it's preferred to use its methods rather than implement
a new function which seems to be faster. It won't work faster in most of the cases. Compare first_word_2 and
first_word_4 for example.
2.Despite the fact first_word_1 (which uses .split() method) looks nice and concise it works worse with long strings
than first_word_2 and first_word_3 do(they use .find() and .index() methods respectively). Especially in case there are
lots of spaces in the text.
3.str.index() method works a bit faster than str.find() but only in case there is a space in the text. Otherwise it's
needed to handle an exception which takes some extra time.
Thus, I'd use str.find() method in such kind of tasks.
"""
只能說我還太菜了，要再多練練
僅此紀錄
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