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儘管相同的代碼運行兩次，爲什麼Python代碼以極大不同的速度運行？Python線剖析器結果不一致
代碼
我正在做一些剖析短暫Python代碼：
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, "")
測試
我使用line_profiler用命令kernprof -l -v test.py。我多次測試此代碼，並且所有結果都不一致。
測試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)
試驗2（I編輯的代碼）：
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)
試驗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)
這是我發現令人困惑的部分。 最初花費44s運行的過程現在需要4s才能運行。我還注意到，無論何時編輯文件，都需要很長時間才能再次運行。這裏有三個以上的測試證明了我的觀點：
編輯後的第一個測試：編輯後
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)
二測：編輯後
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)
第三個測試（其類似於第二個測試）：
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)