<p>就我个人而言,只要我在理解中有更多的非琐碎的东西(例如2<code>for</code>和1<code>if</code>),我就会使用生成器函数。你知道吗</p>
<p>例如,在您的案例中,您可以使用(我认为它更具可读性,但这可能是主观的):</p>
<pre><code>def double_evens(inp):
for item in inp:
if item % 2 == 0:
yield item
yield item
</code></pre>
<p>试运行:</p>
<pre><code>>>> list(double_evens(range(10)))
[0, 0, 1, 2, 2, 3, 4, 4, 5, 6, 6, 7, 8, 8, 9]
</code></pre>
<hr/>
<p>请注意,这种方法甚至可以更快(它比答案中的其他解决方案快3倍,比你在我的电脑上的理解快2倍)。从<a href="https://stackoverflow.com/a/44468758/5393381">this answer</a>获取计时框架:</p>
<pre><code>from itertools import chain
def coldspeed1(mylist):
return [y for x in mylist for y in [x] * (2 - x % 2)]
def coldspeed2(mylist):
return list(chain.from_iterable([x] * (2 - x % 2) for x in mylist))
def double_evens(inp):
for item in inp:
if not item % 2:
yield item
yield item
def mseifert(inp):
return list(double_evens(inp))
def ettanany(my_list):
new_list = [[i] * 2 if i % 2 == 0 else i for i in my_list]
res = []
for i in new_list:
if isinstance(i, list):
res.extend(i)
else:
res.append(i)
return res
def no1xsyzy(original):
return [i for x in original for i in ([x,x] if x%2 == 0 else [x])]
# Timing setup
timings = {coldspeed1: [], coldspeed2: [], mseifert: [], ettanany: [], no1xsyzy: []}
sizes = [2**i for i in range(1, 20, 2)]
# Timing
for size in sizes:
mylist = list(range(size))
for func in timings:
res = %timeit -o func(mylist)
timings[func].append(res)
# Plotting
%matplotlib notebook
import matplotlib.pyplot as plt
import numpy as np
fig = plt.figure(1)
ax = plt.subplot(111)
baseline = mseifert # choose one function as baseline
for func in timings:
ax.plot(sizes,
[time.best / ref.best for time, ref in zip(timings[func], timings[baseline])],
label=str(func.__name__))
#ax.set_yscale('log')
ax.set_xscale('log')
ax.set_xlabel('size')
ax.set_ylabel('time relative to {}'.format(baseline.__name__))
ax.grid(which='both')
ax.legend()
plt.tight_layout()
</code></pre>
<p><a href="https://i.stack.imgur.com/x4tFr.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/x4tFr.png" alt="enter image description here"/></a></p>
<p>此图绘制了与我的解决方案相比的相对时间差。请注意,x轴(大小)是对数的,而y轴(时差)不是</p>