In-depth grasp of the skills of using the Python built-in debug library pdb

Python debugging tool pdb (Python Debugger) is Python's built-in debugger, which allows developers to check and modify the state of the program during code execution.

Mastering the skills of using pdb is essential to improve development efficiency and solve complex problems.

This article will introduce the basic usage, advanced skills and specific applications of pdb in actual development in detail to help you become a real Python debugger.

Getting started with the basics.

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Start pdb.

To start pdb in code, insert the following code where you need to debug:

import pdb; pdb.set_trace()

When the program runs to this line, it pauses and enters pdb interaction mode.

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Common commands.

1. # h (elp) #: Display help information.

2. # l (ist) #: Display the source code of the current line.

3. # n (ext) #: Execute the next line of code.

4. # c (ontinue) #: Continue to execute the program until the next breakpoint is encountered or the program ends.

5. # s (tep) #: Go inside the function.

6. # r (turn) #: Run to the current function and return.

7. # q (uit) #: Exit the debugger.

8. # p (rint) #: Print the value of the variable.

For example p variable_name。

9. # b (reak) #: Set a breakpoint.

For example b filename:lineno。

10. # cl (ear) #: Clear breakpoints.

For example cl filename:lineno。

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Sample code.

The following is a simple example of how to debug with pdb:

def add(a, b):
    return a + b

def main():
    x = 10
    y = 20
    import pdb; pdb.set_trace()  # 设置断点
    result = add(x, y)
    print(f"Result: {result}")

if __name__ == "__main__":
    main()

After running the above code, the program will pdb.set_trace()Pause and enter pdb interaction mode.

You can use the aforementioned commands to check and modify program state.

Advanced skills.

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Conditional breakpoint.

Sometimes you may just want to pause the program under certain conditions, when conditional breakpoints can be used.

E.g:

import pdb; pdb.set_trace()
# 假设我们想在 x > 10 时暂停
if x > 10:
    pdb.set_trace()

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View the call stack.

During debugging, understanding the call stack can help you better understand the execution flow of the program.

Use w(here)The command can view the current call stack:

(Pdb) w

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Modify the variable value.

You can directly modify the value of the variable during debugging to test the program behavior in different situations.

E.g:

(Pdb) p x
10
(Pdb) x = 20
(Pdb) p x
20

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Catch exceptions.

Sometimes the program may throw an exception, using post-mortemDebug mode allows you to enter debug mode immediately after an exception occurs:

import pdb; pdb.pm()

Or catch the exception in the code and enter debug mode:

try:
    # 可能抛出异常的代码
except Exception as e:
    import pdb; pdb.post_mortem()

Applications in actual development.

In actual development, pdb can help you quickly locate and fix bugs.

The following are some common application scenarios: \n#

Debug loops and recursion.

When dealing with complex loops or recursions, pdb can help you track the execution of each step step step by step.

E.g:

def factorial(n):
    if n == 0:
        return 1
    else:
        return n * factorial(n-1)

def main():
    import pdb; pdb.set_trace()
    result = factorial(5)
    print(f"Factorial: {result}")

if __name__ == "__main__":
    main()

By step-by-step factorialFunction, you can clearly see the calculation process of each step.

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Debug multi-threaded programs.

When debugging multi-threaded programs, pdb can help you view and control the execution status of each thread.

E.g:

import threading
import time
import pdb; pdb.set_trace()

def worker():
    for i in range(5):
        time.sleep(1)
        print(f"Worker: {i}")

threads = []
for i in range(3):
    t = threading.Thread(target=worker)
    threads.append(t)
    t.start()

for t in threads:
    t.join()

By setting breakpoints in the main thread, you can view and control the execution of all child threads.

Summarize.

Pdb is a powerful debugging tool built into Python. Mastering its basic usage and advanced skills is essential to improve development efficiency and solve complex problems.

Through the introduction of this article, I hope you can use pdb proficiently for efficient debugging and become a real Python debugger.

In actual development, flexible use of the various functions of pdb will greatly improve your programming ability and problem-solving ability.