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HomeBackend DevelopmentPython Tutorialpython中实现php的var_dump函数功能

最近在做python的web开发(原谅我的多变,好东西总想都学着。。。node.js也是),不过过程中总遇到些问题,不管是web.py还是django,开发起来确实没用php方便,毕竟存在的时间比较短,很多不完善的地方。

比如我在调试php中最常用的函数,var_dump,在python里找不到合适的替代函数。php中var_dump是一个特别有用的函数,它可以输出任何变量的值,不管你是一个对象还是一个数组,或者只是一个数。它总能用友好的方式输出,我调试的时候经常会需要看某位置的变量信息,调用它就很方便:

但是开发python的时候就没有太好的替代方案。

之前想到repr,但这个函数只是调用了对象中的__str__,和直接print obj没啥区别。print是打印它,而repr是将其作为值返回。如果对象所属的类没有定义__str__这个函数,那么返回的就会是难看的一串字符。

后来又想到了vars 函数,vars函数是python的内建函数,专门用来输出一个对象的内部信息。但这个对象所属的类中必须有__dict__函数。一般的类都有这个dict,但像[]和{}等对象就不存在这个dict,这样调用vars函数就会抛出一个异常:

复制代码 代码如下:

Traceback (most recent call last):
  File "", line 1, in
TypeError: vars() argument must have __dict__ attribute

所以后来几经寻找,找到一个个比较好,功能能够与var_dump类似的函数如下:

复制代码 代码如下:

def dump(obj):
  '''return a printable representation of an object for debugging'''
  newobj=obj
  if '__dict__' in dir(obj):
    newobj=obj.__dict__
    if ' object at ' in str(obj) and not newobj.has_key('__type__'):
      newobj['__type__']=str(obj)
    for attr in newobj:
      newobj[attr]=dump(newobj[attr])
  return newobj

这是使用方式:

复制代码 代码如下:

 class stdClass(object): pass
obj=stdClass()
obj.int=1
obj.tup=(1,2,3,4)
obj.dict={'a':1,'b':2, 'c':3, 'more':{'z':26,'y':25}}
obj.list=[1,2,3,'a','b','c',[1,2,3,4]]
obj.subObj=stdClass()
obj.subObj.value='foobar'

from pprint import pprint
pprint(dump(obj))

最后输出是:

复制代码 代码如下:

{'__type__': '<__main__.stdclass object at>',
 'dict': {'a': 1, 'c': 3, 'b': 2, 'more': {'y': 25, 'z': 26}},
 'int': 1,
 'list': [1, 2, 3, 'a', 'b', 'c', [1, 2, 3, 4]],
 'subObj': {'__type__': '<__main__.stdclass object at>',
            'value': 'foobar'},
 'tup': (1, 2, 3, 4)}   

然后github有个开源的module,可以参考:https://github.com/sha256/python-var-dump

说一下pprint这个函数,他是一个人性化输出的函数,会将要输出的内容用程序员喜欢的方式输出在屏幕上。参阅这篇文章比较好理解:http://www.jb51.net/article/60143.htm

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