Python：自动更改变量内容

发布于 2024-08-19 18:28:31 字数 591 浏览 10 评论 0原文

我有一个 Python 函数，它接收大量变量，并根据它们构建 SQL 查询：

def myfunc(name=None, abbr=None, grade=None, ...)

这些值应该构建 SQL 查询。，那些等于 None 的值应该更改为 NULL，而那些存储有用值的值应该用 ' 括起来：

name="'"+name+"\'" if name else 'NULL'
abbr="'"+abbr+"\'" if abbr else 'NULL'
...
Lots of lines here - that's my problem!
...

为此，

query="""INSERT INTO table(name, abbr, ...)
         VALUES (%(name)s, %(abbr)s, ...) """ locals()
cur.execute(query)

有没有更好、更Pythonic的方式来根据这个规则改变变量内容？

亚当

原文

I have a Python function which receives numerous variables, and builds an SQL query out of them:

def myfunc(name=None, abbr=None, grade=None, ...)

These values should build an SQL query. For that purpose, Those who equal None should be changed to NULL, and those who store useful values should be embraced with 's:

name="'"+name+"\'" if name else 'NULL'
abbr="'"+abbr+"\'" if abbr else 'NULL'
...
Lots of lines here - that's my problem!
...

And than,

query="""INSERT INTO table(name, abbr, ...)
         VALUES (%(name)s, %(abbr)s, ...) """ locals()
cur.execute(query)

Is there a nicer, more Pythonic way to change the variable contents according to this rule?

Adam

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吃不饱 2024-08-26 18:28:31

形成 SQL 查询的最佳方法不是通过字符串格式化 - cursor 对象的 execute 方法采用带有占位符的查询字符串和一个序列（或字典，取决于您对 DB API 的具体实现）以及要替换的值；然后它将执行您需要的 None-to-Null 和字符串引用。

我强烈建议您研究一下这种可能性。但是，如果您需要出于其他目的进行字符串处理，您可以执行以下操作：

processed = dict((n, "'%s'" % v if v is not None else 'NULL')
                 for n, v in locals().iteritems())

然后使用字典 processed 而不是 locals() 进行进一步的字符串格式化。

The best way to form a SQL query is not by string-formatting -- the execute method of a cursor object takes a query string with placeholders and a sequence (or dict, depending on the exact implementation you have of the DB API) with the values to substitute there; it will then perform the None-to-Null and string-quoting that you require.

I strongly recommend you look into that possibility. If you need string processing for some other purpose, however, you could do something like:

processed = dict((n, "'%s'" % v if v is not None else 'NULL')
                 for n, v in locals().iteritems())

and then use dictionary processed instead of locals() for further string-formatting.

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_蜘蛛 2024-08-26 18:28:31

您可以如下定义 myfunc：

def myfunc(*args, **kwargs)

其中 kwargs 是一个字典，包含传递给函数的所有命名参数。

要获取查询参数的值，您可以使用 kwargs.get(name_of_parameter, 'NULL')。要构建查询，您只需迭代所有字典项即可。但请注意，如果您这样做，作为命名参数传递给函数的任何参数都将最终出现在查询中。

You could define myfunc as follows:

def myfunc(*args, **kwargs)

Where kwargs is a dictionary holding all named parameters passed to the function.

To get the value of a query parameter, you would use kwargs.get(name_of_parameter, 'NULL'). To build the query, you would just iterate over all dictionary items. Note however, that any parameter passed as a named parameter to the function will end up in the query if you do it this way.

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