为什么尽管相同的代码运行两次，python 代码的运行速度却截然不同？
代码
我正在为一个简短的 Python 代码做一些分析：
import urllib3
@profile
def download(url, file_path):
http = urllib3.PoolManager()
r = http.request("GET", url)
print("FINISHED GET!")
print("WRITING TO "+file_path)
with open(file_path, "wb") as f:
f.write(r.data)
r.release_conn()
url = "http://interactivepaper.todayonline.com/jrsrc/260516/260516.pdf"
download(url, "")
测试
我正在使用line_profiler命令kernprof -l -v test.py。我多次测试了这段代码，所有结果都不一致。
测试1：
FINISHED GET!
WRITING TO
Wrote profile results to test.py.lprof
Timer unit: 1e-06 s
Total time: 44.653 s
File: test.py
Function: download at line 3
Line # Hits Time Per Hit % Time Line Contents
==============================================================
3 @profile
4 def download(url, file_path):
5 1 273 273.0 0.0 http = urllib3.PoolManager()
6 1 44652667 44652667.0 100.0 r = http.request("GET", url)
7 1 37 37.0 0.0 print("FINISHED GET!")
8 1 4 4.0 0.0 print("WRITING TO "+file_path)
9 1 29 29.0 0.0 with open(file_path, "wb") as f:
10 f.write(r.data)
11 r.release_conn()
(There was an IO Error from here onwards as I used an empty string)
测试 2（我编辑了代码）：
FINISHED GET!
WRITING TO
Wrote profile results to test.py.lprof
Timer unit: 1e-06 s
Total time: 44.6693 s
File: test.py
Function: download at line 3
Line # Hits Time Per Hit % Time Line Contents
==============================================================
3 @profile
4 def download(url, file_path):
5 1 186 186.0 0.0 http = urllib3.PoolManager()
6 1 44669082 44669082.0 100.0 r = http.request("GET", url)
7 1 42 42.0 0.0 print("FINISHED GET!")
8 1 4 4.0 0.0 print("WRITING TO "+file_path)
测试 3：
FINISHED GET!
WRITING TO
Wrote profile results to test.py.lprof
Timer unit: 1e-06 s
Total time: 4.53504 s
File: test.py
Function: download at line 3
Line # Hits Time Per Hit % Time Line Contents
==============================================================
3 @profile
4 def download(url, file_path):
5 1 262 262.0 0.0 http = urllib3.PoolManager()
6 1 4534736 4534736.0 100.0 r = http.request("GET", url)
7 1 37 37.0 0.0 print("FINISHED GET!")
8 1 4 4.0 0.0 print("WRITING TO "+file_path)
这是我感到困惑的部分。最初需要 44 秒运行的进程现在需要 4 秒才能运行。我还注意到，每当我编辑文件时，再次运行都需要很长时间。这里有另外三个测试证明我的观点：
编辑后的第一次测试：
Wrote profile results to test.py.lprof
Timer unit: 1e-06 s
Total time: 49.7018 s
File: test.py
Function: download at line 3
Line # Hits Time Per Hit % Time Line Contents
==============================================================
3 @profile
4 def download(url, file_path):
5 1 187 187.0 0.0 http = urllib3.PoolManager()
6 1 49701585 49701585.0 100.0 r = http.request("GET", url)
编辑后的第二次测试：
Timer unit: 1e-06 s
Total time: 9.10985 s
File: test.py
Function: download at line 3
Line # Hits Time Per Hit % Time Line Contents
==============================================================
3 @profile
4 def download(url, file_path):
5 1 185 185.0 0.0 http = urllib3.PoolManager()
6 1 9109665 9109665.0 100.0 r = http.request("GET", url)
编辑后的第三次测试（类似于第二次测试）：
Wrote profile results to test.py.lprof
Timer unit: 1e-06 s
Total time: 12.9593 s
File: test.py
Function: download at line 3
Line # Hits Time Per Hit % Time Line Contents
==============================================================
3 @profile
4 def download(url, file_path):
5 1 189 189.0 0.0 http = urllib3.PoolManager()
6 1 12959072 12959072.0 100.0 r = http.request("GET", url)