我是Python新手,我想确保我正确地重写了__eq__
和__hash__
,以免以后引起痛苦的错误:
(我正在使用谷歌应用引擎。)
class Course(db.Model):
dept_code = db.StringProperty()
number = db.IntegerProperty()
title = db.StringProperty()
raw_pre_reqs = db.StringProperty(multiline=True)
original_description = db.StringProperty()
def getPreReqs(self):
return pickle.loads(str(self.raw_pre_reqs))
def __repr__(self):
title_msg = self.title if self.title else "Untitled"
return "%s %s: %s" % (self.dept_code, self.number, title_msg)
def __attrs(self):
return (self.dept_code, self.number, self.title, self.raw_pre_reqs, self.original_description)
def __eq__(self, other):
return isinstance(other, Course) and self.__attrs() == other.__attrs()
def __hash__(self):
return hash(self.__attrs())
稍微复杂一点的类型:
class DependencyArcTail(db.Model):
''' A list of courses that is a pre-req for something else '''
courses = db.ListProperty(db.Key)
''' a list of heads that reference this one '''
forwardLinks = db.ListProperty(db.Key)
def __repr__(self):
return "DepArcTail %d: courses='%s' forwardLinks='%s'" % (id(self), getReprOfKeys(self.courses), getIdOfKeys(self.forwardLinks))
def __eq__(self, other):
if not isinstance(other, DependencyArcTail):
return False
for this_course in self.courses:
if not (this_course in other.courses):
return False
for other_course in other.courses:
if not (other_course in self.courses):
return False
return True
def __hash__(self):
return hash((tuple(self.courses), tuple(self.forwardLinks)))
一切看起来都很好?
更新以反映@Alex的评论
class DependencyArcTail(db.Model):
''' A list of courses that is a pre-req for something else '''
courses = db.ListProperty(db.Key)
''' a list of heads that reference this one '''
forwardLinks = db.ListProperty(db.Key)
def __repr__(self):
return "DepArcTail %d: courses='%s' forwardLinks='%s'" % (id(self), getReprOfKeys(self.courses), getIdOfKeys(self.forwardLinks))
def __eq__(self, other):
return isinstance(other, DependencyArcTail) and set(self.courses) == set(other.courses) and set(self.forwardLinks) == set(other.forwardLinks)
def __hash__(self):
return hash((tuple(self.courses), tuple(self.forwardLinks)))
第一个很好。第二个问题有两个原因:
.courses
中可能有重复项.courses
但不同.forwardLinks
的两个实体将比较相等但具有不同散列我将通过使相等依赖于进程和前向链接来修复第二个链接,但这两个链接都对集合进行了更改(因此没有重复),对于散列也是如此。一、 e.:
这当然是假设前向链接对对象的“真实值”至关重要,否则应该从
__eq__
和__hash__
中省略它们。编辑:从
__hash__
调用tuple
中删除,这些调用充其量是多余的(而且可能是有害的,正如@Mark[[tx]的注释所建议的那样!!!]]);根据@Phillips[[tx]的注释建议,将哈希中的set
更改为frozenset
!!!]].相关问题 更多 >
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