[英]What do double underscores indicate?
In Python I know that double underscores preceding a name cause Python to prepend the classname
to the variable
name as in _classname__variable
name (name mangling). 在Python中,我知道在名称前加双下划线会导致Python在classname
名之前加variable
名,就像_classname__variable
name(名称_classname__variable
)一样。 So my question is this, in an Python/Django app I have been asked to modify, there are variable(?) names of the type tr_rowid_debtor__de_listed_date__lte
. 所以我的问题是,在我被要求修改的Python / Django应用程序中,存在类型为tr_rowid_debtor__de_listed_date__lte
变量(?)名称。 Is this three variables ( tr_rowid_debtor
, de_listed_date
and lte
) or is this some special construct for Python? 这是三个变量( tr_rowid_debtor
, de_listed_date
和lte
)还是这是Python的一些特殊构造? It is occurring in a statement that builds a query string for Django ... 它发生在为Django构建查询字符串的语句中...
query = DeTransaction.objects.select_related().filter(
tr_rowid_debtor__de_listed_date__lte=to_date,
tr_rowid_debtor__de_rowid_client__cl_rowid=in_client
).values(
'tr_rowid_debtor','tr_rowid_debtor__de_listed_date',
'tr_payment_date','tr_account','tr_to_agency','tr_to_client'
)
Any advice here would be appreciated. 这里的任何建议将不胜感激。
The double underscore notation is used by Django's ORM to indicate some sort of separation in a query. Django的ORM使用双下划线符号表示查询中的某种分隔。 In the case of tr_rowid_debtor__de_listed_date__lte
, three things are happening. 对于tr_rowid_debtor__de_listed_date__lte
,正在发生三件事。
tr_rowid_debtor
specifies the attribute on DeTransaction
, which is a relationship based on what happens next tr_rowid_debtor
指定的属性DeTransaction
这是基于接下来会发生什么关系, de_listed_date
specifies the field of the related model to query against de_listed_date
指定要查询的相关模型的字段 lte
says to perform the comparison using <=
(less than or equal to) lte
表示使用<=
(小于或等于)执行比较 It's worth a read of Django's query docs . 值得阅读Django的查询文档 。 The cover these in some detail. 详细介绍这些内容。
As for whether or not this is special to Python, it is not. 至于这是否对Python来说很特殊,不是。 the __
is assigned to a constant called LOOKUP_SEP
. __
被分配给一个名为LOOKUP_SEP
的常量。 The value is used with str.split()
to generate the WHERE
clause for queries. 该值与str.split()
一起使用以生成查询的WHERE
子句。
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