python – 使用库时缩短大型堆栈跟踪

概述我经常使用像 pandas或 matplotlib这样的大型库. 这意味着异常通常会产生长堆栈跟踪. 由于库中的错误极少,并且经常使用我自己的代码,因此在绝大多数情况下我都不需要查看库的详细信息. 一些常见的例子： 熊猫 >>> import pandas as pd>>> df = pd.DataFrame(dict(a=[1,2,3]))>>> df['b'] # Hint: there 我经常使用像 pandas或 matplotlib这样的大型库.

这意味着异常通常会产生长堆栈跟踪.

由于库中的错误极少,并且经常使用我自己的代码,因此在绝大多数情况下我都不需要查看库的详细信息.

一些常见的例子：

熊猫

>>> import pandas as pd>>> df = pd.DataFrame(dict(a=[1,2,3]))>>> df['b'] # Hint: there _is_ no 'b'

在这里,我试图访问一个未知的密钥.这个简单的错误会产生一个包含28行的堆栈跟踪：

Traceback (most recent call last):  file "an_arbitrary_python\lib\site-packages\pandas\core\indexes\base.py",line 2393,in get_loc    return self._engine.get_loc(key)  file "pandas\_libs\index.pyx",line 132,in pandas._libs.index.IndexEngine.get_loc (pandas\_libs\index.c:5239)  file "pandas\_libs\index.pyx",line 154,in pandas._libs.index.IndexEngine.get_loc (pandas\_libs\index.c:5085)  file "pandas\_libs\hashtable_class_helper.pxi",line 1207,in pandas._libs.hashtable.PyObjectHashtable.get_item (pandas\_libs\hashtable.c:20405)  file "pandas\_libs\hashtable_class_helper.pxi",line 1215,in pandas._libs.hashtable.PyObjectHashtable.get_item (pandas\_libs\hashtable.c:20359)KeyError: 'b'During handling of the above exception,another exception occurred:    Traceback (most recent call last):      file "<stdin>",line 1,in <module>      file "an_arbitrary_python\lib\site-packages\pandas\core\frame.py",line 2062,in __getitem__        return self._getitem_column(key)      file "an_arbitrary_python\lib\site-packages\pandas\core\frame.py",line 2069,in _getitem_column        return self._get_item_cache(key)      file "an_arbitrary_python\lib\site-packages\pandas\core\generic.py",line 1534,in _get_item_cache        values = self._data.get(item)      file "an_arbitrary_python\lib\site-packages\pandas\core\internals.py",line 3590,in get        loc = self.items.get_loc(item)      file "an_arbitrary_python\lib\site-packages\pandas\core\indexes\base.py",line 2395,in get_loc        return self._engine.get_loc(self._maybe_cast_indexer(key))      file "pandas\_libs\index.pyx",in pandas._libs.index.IndexEngine.get_loc (pandas\_libs\index.c:5239)      file "pandas\_libs\index.pyx",in pandas._libs.index.IndexEngine.get_loc (pandas\_libs\index.c:5085)      file "pandas\_libs\hashtable_class_helper.pxi",in pandas._libs.hashtable.PyObjectHashtable.get_item (pandas\_libs\hashtable.c:20405)      file "pandas\_libs\hashtable_class_helper.pxi",in pandas._libs.hashtable.PyObjectHashtable.get_item (pandas\_libs\hashtable.c:20359)    KeyError: 'b'

知道我最终在hashtable_class_helper.pxi中对我来说几乎没用.我需要知道我的代码在哪里搞砸了.

Matplotlib

>>> import matplotlib.pyplot as plt>>> import matplotlib.cm as cm>>> def foo():...     plt.plot([1,3],cbap=cm.Blues) # cbap is a typo for cmap...>>> def bar():...     foo()...>>> bar()

这一次,我的关键字参数中有一个拼写错误.但我仍然需要看到25行堆栈跟踪：

Traceback (most recent call last):  file "<stdin>",in <module>  file "<stdin>",line 2,in bar  file "<stdin>",in foo  file "an_arbitrary_python\lib\site-packages\matplotlib\pyplot.py",line 3317,in plot    ret = ax.plot(*args,**kwargs)  file "an_arbitrary_python\lib\site-packages\matplotlib\__init__.py",line 1897,in inner    return func(ax,*args,**kwargs)  file "an_arbitrary_python\lib\site-packages\matplotlib\axes\_axes.py",line 1406,in plot    for line in self._get_lines(*args,**kwargs):  file "an_arbitrary_python\lib\site-packages\matplotlib\axes\_base.py",line 407,in _grab_next_args    for seg in self._plot_args(remaining,kwargs):  file "an_arbitrary_python\lib\site-packages\matplotlib\axes\_base.py",line 395,in _plot_args    seg = func(x[:,j % ncx],y[:,j % ncy],kw,kwargs)  file "an_arbitrary_python\lib\site-packages\matplotlib\axes\_base.py",line 302,in _makeline    seg = mlines.line2D(x,y,**kw)  file "an_arbitrary_python\lib\site-packages\matplotlib\lines.py",line 431,in __init__    self.update(kwargs)  file "an_arbitrary_python\lib\site-packages\matplotlib\artist.py",line 885,in update    for k,v in props.items()]  file "an_arbitrary_python\lib\site-packages\matplotlib\artist.py",in <Listcomp>    for k,line 878,in _update_property    raise AttributeError('UnkNown property %s' % k)AttributeError: UnkNown property cbap

在这里,我发现我在artist.py中的一行引发了一个引发AttributeError的行,然后直接看到它确实引发了AttributeError.这在信息术语中没有多大价值.

在这些琐碎,互动的例子中,你可能只是说“看看堆栈顶部而不是底部”,但通常我的愚蠢错字发生在一个函数中,所以我感兴趣的行是在某处的中间位置这些库杂乱的堆栈跟踪.

有什么方法可以让这些堆栈跟踪更简洁,并帮助我找到问题的根源,这几乎总是在我自己的代码中,而不是在我碰巧使用的库中？

解决方法 您可以使用 traceback更好地控制异常打印.例如：

import pandas as pdimport tracebacktry:    df = pd.DataFrame(dict(a=[1,3]))    df['b']except Exception,e:    traceback.print_exc(limit=1)    exit(1)

这会触发标准异常打印机制,但只显示堆栈跟踪的第一帧(在您的示例中是您关注的那个).这对我来说产生：

Traceback (most recent call last):  file "t.py",line 6,in <module>    df['b']KeyError: 'b'

显然你会丢失上下文,这在调试自己的代码时很重要.如果我们想要获得幻想,我们可以尝试设计一个测试,看看回溯应该走多远.例如：

def find_depth(tb,continue_test):    depth = 0    while tb is not None:        filename = tb.tb_frame.f_code.co_filename        # Run the test we're given against the filename        if not continue_test(filename):            return depth        tb = tb.tb_next        depth += 1

我不知道你是如何组织和运行你的代码的,但也许你可以这样做：

import pandas as pdimport tracebackimport sysdef find_depth():    # ... code from above here ...try:    df = pd.DataFrame(dict(a=[1,e:    traceback.print_exc(limit=get_depth(        sys.exc_info()[2],# The test for which frames we should include        lambda filename: filename.startswith('my_module')    ))    exit(1)

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