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Python pdb module provides an interactive debugging environment for Developers to debug Python programs. Today we will explore python debugger examples using pdb module and look at the various ways of debugging a python program.

Python pdb模块为开发人员提供调试Python程序的交互式调试环境。 今天，我们将探讨使用pdb模块的python调试器示例，并介绍各种调试python程序的方法。

Python调试器– Py​​thon PDB (Python Debugger – Python PDB)

The pdb module in Python provides us with immense features for effective debugging of python code. This includes:

Python中的pdb模块为我们提供了巨大的功能，可以有效地调试python代码。 这包括：

• Pause a program暂停程序
• Look at the values of variables看一下变量的值
• Look at program execution on every line查看每一行的程序执行

These are just some points that make pdb module a boon for Python programmers. Let’s look at how we can start using this module.

这些只是使pdb模块成为Python程序员的福音的几点。 让我们看看如何开始使用此模块。

启动Python调试器 (Starting Python Debugger)

Well, it isn’t about the program. We can start pdb with any program. Here is a sample program:

好吧，这与程序无关。 我们可以使用任何程序启动pdb。 这是一个示例程序：

class User:def __init__(self, runner):self.counter = runnerdef showSomething(self):for i in range(self.counter):print(i)returnuser = User(5)
user.showSomething()

Let’s see the output for this program:

让我们看一下该程序的输出：

We can go to next line in pdb execution by pressing ‘n’ followed by Enter key.

我们可以通过按“ n”，然后按Enter键转到pdb执行的下一行。

在程序中启动pdb (Starting pdb within the program)

Above example started pdb from the command line, so, pdb tracing started from the very first line of execution. Usually, we only want to debug a specific area of a program which comes much after the program has started.

上面的示例从命令行启动了pdb ，因此pdb跟踪从执行的第一行开始。 通常，我们只想调试程序的特定区域，该区域是在程序启动后很长时间才出现的。

To achieve this, we use pdb in our programs itself. Let’s look at a code snippet:

为此，我们在程序本身中使用了pdb。 让我们看一下代码片段：

import pdbclass User:def __init__(self, runner):self.counter = runnerdef showSomething(self):for i in range(self.counter):pdb.set_trace()print(i)returnuser = User(5)
user.showSomething()

Let’s see the output for this program:

Press n and Enter to go to next line and watch the execution.

让我们看一下该程序的输出：

按n和Enter键转到下一行，观察执行情况。

事后调试 (Post-mortem debugging)

Once the program is finished with the execution process, debugging a failure in it is termed as post-mortem debugging. The module supports this as well with few more functions:

一旦程序完成了执行过程，将其中的故障调试称为事后调试。 该模块还支持以下功能：

import pdbclass User:def __init__(self, runner):self.counter = runnerdef showSomething(self):for i in range(self.runner):pdb.set_trace()print(i)returnuser = User(5)
user.showSomething()

Here, we have mentioned self.runner which doesn’t exist. We can try these functions inside Python interpreter itself:

在这里，我们提到了不存在的self.runner 。 我们可以在Python解释器内部尝试以下功能 ：

检查堆栈上的变量 (Checking variables on the Stack)

One of the points of using a debugger at all is that we should be able to check the program stack and what variables are stored on that stack during program execution. We can do this with pdb as well. Let’s look at a code snippet:

完全使用调试器的要点之一是，我们应该能够检查程序堆栈以及在程序执行期间在堆栈上存储了哪些变量。 我们也可以使用pdb做到这一点。 让我们看一下代码片段：

import pdbdef recursive_calls(i = 5, output = 'somethign here'):if i > 0:recursive_calls(i - 1)else:pdb.set_trace()print(output)returnif __name__ == '__main__':recursive_calls()

This is a simple example for a recursion. Let’s see the output for this program:

这是一个简单的递归示例。 让我们看一下该程序的输出：

Note that we used the where command to print variables on stack. We can also print a specific variable as:

请注意，我们使用where命令在堆栈上打印变量。 我们还可以将特定变量打印为：

For variables which might contain large values like file data etc., we also pretty print the values. So, if the variables is data, we can run the command:

对于可能包含较大值（例如文件数据等）的变量，我们也可以漂亮地打印这些值。 因此，如果变量是data ，我们可以运行以下命令：

pp data

Python pdb断点 (Python pdb Breakpoint)

Using n to go to next line is useful but what if you actually know where to stop? Also, debugging the whole program and moving through each line is tedious when you know where you want to actually stop!

使用n转到下一行很有用，但是如果您实际上知道在哪里停下来怎么办？ 另外，当您知道要实际停止的位置时，调试整个程序并在每一行中移动都是很麻烦的！

With pdb, we can also use breakpoints. For this, we need to inform pdb which line to set a breakpoint to. Here is a sample program and demonstration:

使用pdb，我们还可以使用断点。 为此，我们需要通知pdb将断点设置pdb一行。 这是一个示例程序和演示：

import pdbdef recursive_calls(i = 5, output = 'somethign here'):if i > 0:recursive_calls(i - 1)else:print(output)returnif __name__ == '__main__':recursive_calls()

Nothing unusual here actually. Let’s see the demonstration with this program:

We used the break keyword along with the line number where we want to set the breakpoint.

实际上没有什么异常。 让我们看一下该程序的演示：

我们将break关键字与要设置断点的行号一起使用。

管理断点 (Managing Breakpoints)

As we saw in the last demonstration, when we applied a breakpoint to a line, it was assigned an identifier as Breakpoint 1. The numeric part can be used as an ID to enable and disable these breakpoints interactively. Disabling a breakpoint with disable keyword informs the debugger not to halt execution when that line is reached. The breakpoint is still stored but ignored.

正如在上一个演示中所看到的，当我们将断点应用于行时，它被分配了一个标识符作为Breakpoint 1 。 数字部分可以用作ID，以交互方式启用和禁用这些断点。 使用disable关键字禁用断点会通知调试器在到达该行时不要停止执行。 断点仍被存储但被忽略。

Let’s see how this is done:

让我们看看如何做到这一点：

结论 (Conclusion)

In this post on python debugging, we saw how we can effectively debug a Python program and identify any issues we face using pdb module.

在有关python调试的这篇文章中，我们看到了如何有效地调试Python程序并使用pdb模块确定遇到的任何问题。

Reference: API Doc

参考： API文档

翻译自: https://www.journaldev.com/19114/python-debugger-python-pdb

手机怎么安装py thon