如何在tkinter.Tcl().eval()中捕获自定义TclError错误信息

我使用Python 3.9.15版本，通过tkinter.Tcl实现了一个简易Tcl解析器，解析功能正常，但在实现解析失败处理逻辑时，无法获取抛出的TclError中包含的自定义错误信息。

解析器代码 #

import tkinter as tk
from tkinter import Tcl

def default_command_func(*args):
    print(f'default_command_func : {args}')
    return 'success'

class TclParser(object):
    def __init__(self, data_cls) -> None:
        self.interp = tk.Tcl()
        self.data_cls = data_cls
        self.commands = {}
    
    def register_tcl_command(self, command_name, command_func):
        self.commands[command_name] = command_func
    
    def register_tcl_command_impl(self, command_name, command_func, data_base):
        def wrapper(*args):
            return command_func(data_base, args)
        
        self.interp.createcommand(command_name, wrapper)
        
    def parse_tcl(self, tcl_path):
        with open(tcl_path, 'r') as file:
            tcl_file = file.read()
        data_base = self.data_cls()
        for command_name, command_func in self.commands.items():
            self.register_tcl_command_impl(command_name, command_func, data_base)
                
        try:
            self.interp.eval(tcl_file)
        except tk.TclError as e:
            print(f'unknow error : {str(e)}')
        
        return data_base

测试代码 #

def wrapped_cmd(data_base, args):
    if "error" in args:
        raise tk.TclError("Custom error: Invalid arguments passed")
    else:
        print(f"Executing custom command with args: {args}")
        return "success"


tcl_script = """
custom_cmd arg1 arg2
custom_error error
"""

with open("test.tcl", "w") as f:
    f.write(tcl_script)

parser = TclParser(int)
parser.register_tcl_command('custom_cmd', wrapped_cmd)
parser.register_tcl_command('custom_error', wrapped_cmd)
tech = parser.parse_tcl("test.tcl")

当前输出 #

Executing custom command with args: ('arg1', 'arg2')
unknow error : 

期望输出 #

Executing custom command with args: ('arg1', 'arg2')
parse tcl failed due to: Custom error: Invalid arguments passed
unknow error : Custom error: Invalid arguments passed

解决方案 #

问题出在Python函数中直接抛出TclError时，Tcl解释器并未正确捕获并传递错误信息。需要在命令包装函数中主动调用Tcl解释器的error命令来设置错误状态，而非直接抛出Python异常。

修改代码 #

1. 调整register_tcl_command_impl中的包装函数，添加异常捕获并调用Tcl的error命令：

def register_tcl_command_impl(self, command_name, command_func, data_base):
    def wrapper(*args):
        try:
            return command_func(data_base, args)
        except tk.TclError as e:
            # 将自定义错误信息传递给Tcl解释器
            self.interp.call('error', str(e))
    
    self.interp.createcommand(command_name, wrapper)

2. 优化parse_tcl中的异常处理输出：

try:
    self.interp.eval(tcl_file)
except tk.TclError as e:
    print(f'parse tcl failed due to: {str(e)}')
    print(f'unknow error : {str(e)}')

修改后输出 #

Executing custom command with args: ('arg1', 'arg2')
parse tcl failed due to: Custom error: Invalid arguments passed
unknow error : Custom error: Invalid arguments passed

原理说明 #

当在Python实现的Tcl命令中调用self.interp.call('error', msg)时，会触发Tcl解释器的错误机制，该错误会被上层的self.interp.eval()捕获并转换为tk.TclError异常，此时异常中就会包含自定义错误信息。直接抛出TclError无法关联到Tcl解释器的错误状态，导致信息丢失。

内容的提问来源于stack exchange，提问作者heixxxx