Debug

Debugging 
 assert 
 
 主要用在開發與測試階段 
 可用在程式的條件測試 
 assert <condition>, <message> : 如果 condition 為 True，沒有作用；如果為 False，會產生錯誤，並顯示訊息 
 跳過所有 assert 語句，可以使用 python -O sample.py 。 
 
 檢查變數的值 
 x = 5
assert x == 5, "x should be 5"

assert type(username) == str, "username must be a string" 
 def calculate_square_root(x):
 assert x >= 0, "The input must be non-negative."
 return x ** 0.5

print(calculate_square_root(4)) # 輸出: 2.0
print(calculate_square_root(-1)) # 引發 AssertionError 並顯示 "The input must be non-negative." 
 檢查函示回傳值有無偶數 
 def get_even_number(numbers):
 for num in numbers:
 if num % 2 == 0:
 return num
 assert False, "No even number found in the list."

numbers = [1, 3, 5, 7, 10]
print(get_even_number(numbers)) # 輸出: 10
numbers = [1, 3, 5, 7]
print(get_even_number(numbers)) # 引發 AssertionError 並顯示 "No even number found in the list." 
   
 prinf debugging 
 print("Processing {}".format(basename)) 
 strace 
 
 Linux strace Command Tutorial for Beginners (8 Examples) 
 
 # Installation on RHEL if it's not installed
yum install strace

# Tracing system calls made by a program
strace ./my-program.py
strace -o my-program.strace ./my-program 
 Crash 
 pdb 
 功能： 
 
 設定程式中斷點 
 逐行檢查程式碼 
 檢查變數 
 以互動方式評估表達式 
 
 pdb3 myprog.py 
 pdb-subcommands 
 
 continue : 繼續執行直到異常的程式碼 
 print() : 輸出變數的內容 
 
 (Pdb) continue
...
(Pdb) print(row) 
 Step 1: Set a breakpoint 
 import pdb

def add_numbers(a, b):
 pdb.set_trace() # This will set a breakpoint in the code
 result = a + b
 return result

print(add_numbers(3, 4)) 
 Setp 2: Enter the interactive debugger 
 
 
 a (args): Show the arguments of the current function. 
 
 
 b: Manually set a persistent breakpoint while in debugger. 
 
 
 n (next): Execute the next line within the current function. 
 
 
 s (step): Execute the current line and stop at the first possible occasion (e.g., in a function that is called). 
 
 
 c (continue): Resume normal execution until the next breakpoint. 
 
 
 p (print): Evaluate and print the expression, e.g., p variable_name will print the value of variable_name . 
 
 
 Pp (pretty-print): Pretty-print the value of the expression. 
 
 
 q (quit): Exit the debugger and terminate the program. 
 
 
 r (return): Continue execution until the current function returns. 
 
 
 tbreak: Manually set a temporary breakpoint that goes away once hit the first time. 
 
 
 ! : Prefix to execute an arbitrary Python command in the current environment, e.g., !variable_name = " new_value " will set variable_name to " new_value ". 
 
 
 Step 3: Inspect variables 
 To inspect the variables, simply type the single character, p , then the variable name to see its current value. For instance, if you have a variable in your code named sentiment_score , just type p sentiment_score at the pdb prompt to inspect its value. 
 Step 4: Modify variables 
 A big advantage of pdb is that you can change the value of a variable directly in the debugger. For example, to change sentiment_score to 0.9, you'd type !sentiment_score = 0.9 . 
 To confirm these changes, use a or directly probe the value with p <value name> . 
  Step 5: Exit the debugger 
 When you’re done, simply enter q (quit) to exit the debugger and terminate the program. 
 Post-mortem debugging 
 python -m pdb your_script.py 
 Memory Leaks 
 當不再需要的記憶體未釋放時，就會發生記憶體洩漏。即使重新啟動，仍需要大量記憶體的應用程式，很可能指向記憶體洩漏 
 memory_profiler 
 第一欄顯示每一行執行時所需的記憶體數量。第二欄顯示每一行所增加的記憶體 
 python3 -m memory_profiler myprog.py 
 In Code 
 
 在 main() 上方加上 @profile 標籤 
 @ 標籤稱為 Decorator: 在 Python 中使用它來為函數增加額外的行為，而不需要修改程式碼 
 memory-profiler 
 
 from memory_profiler import profile

...
...

@profile
def main():
 ...
 ...