Python之namedtuple源码分析
namedtuple()函数根据提供的参数创建一个新类，这个类会有一个类名，一些字段名和一个可选的用于定义类行为的关键字，具体实现如下
namedtuple函数源码
from keyword import iskeyword as _iskeyword import sys as _sys import logging logging.basicConfig(level=logging.INFO, filename="logging.txt", filemode="w+", \ format = '%(asctime)s - %(name)s - %(levelname)s - %(message)s') logger = logging.getLogger(__name__) _class_template = """\ from builtins import property as _property, tuple as _tuple from operator import itemgetter as _itemgetter from collections import OrderedDict class {typename}(tuple): '{typename}({arg_list})' __slots__ = () _fields = {field_names!r} def __new__(_cls, {arg_list}): 'Create new instance of {typename}({arg_list})' return _tuple.__new__(_cls, ({arg_list})) @classmethod def _make(cls, iterable, new=tuple.__new__, len=len): 'Make a new {typename} object from a sequence or iterable' result = new(cls, iterable) if len(result) != {num_fields:d}: raise TypeError('Expected {num_fields:d} arguments, got %d' % len(result)) return result def _replace(_self, **kwds): 'Return a new {typename} object replacing specified fields with new values' result = _self._make(map(kwds.pop, {field_names!r}, _self)) if kwds: raise ValueError('Got unexpected field names: %r' % list(kwds)) return result def __repr__(self): 'Return a nicely formatted representation string' return self.__class__.__name__ + '({repr_fmt})' % self def _asdict(self): 'Return a new OrderedDict which maps field names to their values.' return OrderedDict(zip(self._fields, self)) def __getnewargs__(self): 'Return self as a plain tuple. Used by copy and pickle.' return tuple(self) {field_defs} """ _repr_template = '{name}=%r' _field_template = '''\ {name} = _property(_itemgetter({index:d}), doc='Alias for field number {index:d}') ''' def namedtuple(typename, field_names, *, verbose=False, rename=False, module=None): """Returns a new subclass of tuple with named fields. >>> Point = namedtuple('Point', ['x', 'y']) >>> Point.__doc__ # docstring for the new class 'Point(x, y)' >>> p = Point(11, y=22) # instantiate with positional args or keywords >>> p[0] + p[1] # indexable like a plain tuple 33 >>> x, y = p # unpack like a regular tuple >>> x, y (11, 22) >>> p.x + p.y # fields also accessible by name 33 >>> d = p._asdict() # convert to a dictionary >>> d['x'] 11 >>> Point(**d) # convert from a dictionary Point(x=11, y=22) >>> p._replace(x=100) # _replace() is like str.replace() but targets named fields Point(x=100, y=22) """ # Validate the field names. At the user's option, either generate an error # message or automatically replace the field name with a valid name. if isinstance(field_names, str): field_names = field_names.replace(',', ' ').split() field_names = list(map(str, field_names)) typename = str(typename) logging.info("%s: %s" %(typename, field_names)) if rename: seen = set() for index, name in enumerate(field_names): if (not name.isidentifier() or _iskeyword(name) or name.startswith('_') or name in seen): field_names[index] = '_%d' % index seen.add(name) for name in [typename] + field_names: logging.info(name) if type(name) is not str: raise TypeError('Type names and field names must be strings') #判断是否为标识符，标识符必须以字母或者“_”开头 #标识符用于作为变量，函数名、类名、方法名等 if not name.isidentifier(): raise ValueError('Type names and field names must be valid ' 'identifiers: %r' % name) #判断是否为关键字，关键字为python内部已经使用了的标识符 if _iskeyword(name): raise ValueError('Type names and field names cannot be a ' 'keyword: %r' % name) seen = set() for name in field_names: if name.startswith('_') and not rename: raise ValueError('Field names cannot start with an underscore: ' '%r' % name) if name in seen: raise ValueError('Encountered duplicate field name: %r' % name) seen.add(name) # Fill-in the class template class_definition = _class_template.format( typename = typename, field_names = tuple(field_names), num_fields = len(field_names), arg_list = repr(tuple(field_names)).replace("'", "")[1:-1], repr_fmt = ', '.join(_repr_template.format(name=name) for name in field_names), field_defs = '\n'.join(_field_template.format(index=index, name=name) for index, name in enumerate(field_names)) ) logging.info(class_definition) # Execute the template string in a temporary namespace and support # tracing utilities by setting a value for frame.f_globals['__name__'] namespace = dict(__name__='namedtuple_%s' % typename) exec(class_definition, namespace) result = namespace[typename] result._source = class_definition if verbose: print(result._source) # For pickling to work, the __module__ variable needs to be set to the frame # where the named tuple is created. Bypass this step in environments where # sys._getframe is not defined (Jython for example) or sys._getframe is not # defined for arguments greater than 0 (IronPython), or where the user has # specified a particular module. if module is None: try: module = _sys._getframe(1).f_globals.get('__name__', '__main__') except (AttributeError, ValueError): pass if module is not None: result.__module__ = module return result
通过函数模板字符串_class_template.format()会生成我们需要的实例类：
eg: people = namedtuple("person","name,age,sex")
class person(tuple) 分析
#coding=utf-8 from builtins import property as _property, tuple as _tuple from operator import itemgetter as _itemgetter from collections import OrderedDict import logging logging.basicConfig(level=logging.INFO, filename="logging.txt", filemode="w+", \ format = '%(asctime)s - %(name)s - %(levelname)s - %(message)s') logger = logging.getLogger(__name__) class person(tuple): 'person(name, age, sex)' __slots__ = () _fields = ('name', 'age', 'sex') def __new__(_cls, name, age, sex): 'Create new instance of person(name, age, sex)' logger.info("__new__") return _tuple.__new__(_cls, (name, age, sex)) @classmethod def _make(cls, iterable, new=tuple.__new__, len=len): 'Make a new person object from a sequence or iterable' result = new(cls, iterable) if len(result) != 3: raise TypeError('Expected 3 arguments, got %d' % len(result)) return result def _replace(_self, **kwds): 'Return a new person object replacing specified fields with new values' #需要深刻理解该代码的精髓 logger.info(type(_self)) for item in _self: logger.info(item) str = ''' how to replace dict_keyvalue li = map({"age":99}.pop, ('name', 'age', 'sex'), ("zhanglin", "11", "man")) ''' logger.info(str) result = _self._make(map(kwds.pop, ('name', 'age', 'sex'), _self)) if kwds: raise ValueError('Got unexpected field names: %r' % list(kwds)) return result def __repr__(self): 'Return a nicely formatted representation string' return self.__class__.__name__ + '(name=%r, age=%r, sex=%r)' % self def _asdict(self): 'Return a new OrderedDict which maps field names to their values.' return OrderedDict(zip(self._fields, self)) #打包为元组列表 def __getnewargs__(self): 'Return self as a plain tuple. Used by copy and pickle.' return tuple(self) name = _property(_itemgetter(0), doc='Alias for field number 0') age = _property(_itemgetter(1), doc='Alias for field number 1') sex = _property(_itemgetter(2), doc='Alias for field number 2') if __name__ == "__main__": p1 = person("zhanglin", "30", "man") logger.info("{0}:{1}".format("p1", p1)) #_replace验证 p2 = p1._replace(name ="zhangsan", age=99) logger.info(p2) logger.info("{0}:{1}".format("p2", p2))
测试结果：
2018-03-21 15:10:46,197 - __main__ - INFO - __new__ 2018-03-21 15:10:46,197 - __main__ - INFO - p1:person(name='zhanglin', age='30', sex='man') 2018-03-21 15:10:46,197 - __main__ - INFO - <class '__main__.person'> 2018-03-21 15:10:46,197 - __main__ - INFO - zhanglin 2018-03-21 15:10:46,197 - __main__ - INFO - 30 2018-03-21 15:10:46,197 - __main__ - INFO - man 2018-03-21 15:10:46,197 - __main__ - INFO - how to replace dict_keyvalue li = map({"age":99}.pop, ('name', 'age', 'sex'), ("zhanglin", "11", "man")) 2018-03-21 15:10:46,197 - __main__ - INFO - person(name='zhangsan', age=99, sex='man') 2018-03-21 15:10:46,197 - __main__ - INFO - p2:person(name='zhangsan', age=99, sex='man')
根据类的字符串模板创建类
#coding=utf-8 import logging logging.basicConfig(level=logging.INFO, filename="logging.txt", filemode="w+",\ format = '%(asctime)s - %(name)s - %(levelname)s - %(message)s') logger = logging.getLogger(__name__) _class_template = \ ''' class {typename}(tuple): __slots__ = () _fields = {field_names!r} def __new__(cls, *args, **dwargs): return super().__new__(cls, *args, **dwargs) ''' def defineclass(typename, field_names): logging.info(field_names) class_definition = _class_template.format(typename=typename,field_names=field_names,\ #方法1 arg_list = ','.join(name for name in field_names),\ self_format = "".join("\t\tself.{name}={name}\n".format(name=name) for name in field_names)) #方法2 #arg_list = ', '.join('{name}'.format(name=name) for name in field_names)) #方法3 #arg_list = repr(tuple(field_names)).replace("'", "")[1:-1]) logging.info(class_definition) namespace = dict(__name__='defineclass_%s' % typename) logging.info("namespce:{}".format(namespace)) exec(class_definition, namespace) result = namespace[typename] logging.info("typename:{0}--result:{1}".format(typename, namespace[typename])) result._source = class_definition return result if __name__ == "__main__": person = defineclass("person", ("name", "age", "sex")) print (type(person)) p = person(("zhanglin", "31", "man")) print (p) print (p[0])
2018-03-22 00:05:50,705 - root - INFO - ('name', 'age', 'sex') 2018-03-22 00:05:50,705 - root - INFO - class person(tuple): __slots__ = () _fields = ('name', 'age', 'sex') def __new__(cls, *args, **dwargs): return super().__new__(cls, *args, **dwargs) 2018-03-22 00:05:50,705 - root - INFO - namespce:{'__name__': 'defineclass_person'} 2018-03-22 00:05:50,705 - root - INFO - typename:person--result:<class 'defineclass_person.person'>
