python3基于字符串的字典搜索列表

Question

假设我有绳子

"((attr1=25 and attr2=8) or attr3=15)"

或者

^{pr2}$

或者

"(attrXYZ=10)"

甚至是

"(attr1=20 and attr2=20 and attr3=20 and attr4=20)"

以及一个包含字典的列表，其中每个字典在字符串中可能有或没有指定的属性。在Python中有没有一种简单的方法来过滤与这种类型的字符串查询匹配的字典？在

Answer 1

免责声明：这是一个非常懒惰和不安全的解决方案，它使用了Python最不光彩的两个函数eval和{a2}，但如果输出的形状与您提供的完全相同，则可以使用

我们的策略是编辑输入，使其看起来与Python自然理解的语法相似，而不是创建自己的解析器。为此，我们将使用dis模块（Python字节码反汇编程序）来获取字符串中的所有名称。在

import dis 

class Number:
    def __init__(self, n, exists=True):
        self.n = n
        self.exists = exists

    def __lt__(self, other):
        return self.n < other if self.exists else False

    def __le__(self, other):
        return self.n <= other if self.exists else False

    def __eq__(self, other):
        return self.n == other if self.exists else False

    def __ne__(self, other):
        return self.n != other if self.exists else False

    def __gt__(self, other):
        return self.n > other if self.exists else False

    def __ge__(self, other):
        return self.n >= other if self.exists else False


def clear_entries(entry):
    entry_output = entry.replace('!=', '<>').replace('=','==').replace('<>','!=')
    return entry_output

def check_condition(dict_, str_):
    str_ = clear_entries(str_)

    for k, v in dict_.items():
        exec("{0} = {1}".format(k, v))

    all_names = dis.Bytecode(str_).codeobj.co_names
    l_ = locals()
    non_defined_names = [v for v in all_names if v not in l_]

    for name in non_defined_names:
        exec("{0} = Number(0, exists=False)".format(name))  # the number value does not matter here (because of the 'exists' flag)

    if eval(str_):
        return True

    return False

测试

^{pr2}$

结果

(True, '"((attr1=25 and attr2=8) or attr3=15)"', {'attr1': 25, 'attr2': 8, 'attr3': 123})
(False, '"((attr1=25 and attr2=8) or attr3=15)"', {'attr1': 1, 'attr2': 8, 'attr3': 123})
(False, '"((attr1=25 and attr2=8) or attr3=15)"', {'attr1': 26, 'attr2': 8, 'attr3': 123, 'attr4': 1})
(False, '"((attr1=25 and attr2=8) or attr3=15)"', {'attr1': 1, 'attr2': 50, 'attr3': 1, 'attr4': 20})
(False, '"((attr1=25 and attr2=8) or attr3=15)"', {'attr1': -1, 'attr2': 50, 'attr3': 1, 'attr4': 20})
(False, '"((attr1=25 and attr2=8) or attr3=15)"', {'attrXYZ': 3})
(False, '"((attr1=25 and attr2=8) or attr3=15)"', {'attrXYZ': 10})
(False, '"((attr1=25 and attr2=8) or attr3=15)"', {'attr1': 20})
(False, '"((attr1>25 and attr2<50) or (attr3=10 and attr4=20))"', {'attr1': 25, 'attr2': 8, 'attr3': 123})
(False, '"((attr1>25 and attr2<50) or (attr3=10 and attr4=20))"', {'attr1': 1, 'attr2': 8, 'attr3': 123})
(True, '"((attr1>25 and attr2<50) or (attr3=10 and attr4=20))"', {'attr1': 26, 'attr2': 8, 'attr3': 123, 'attr4': 1})
(False, '"((attr1>25 and attr2<50) or (attr3=10 and attr4=20))"', {'attr1': 1, 'attr2': 50, 'attr3': 1, 'attr4': 20})
(False, '"((attr1>25 and attr2<50) or (attr3=10 and attr4=20))"', {'attr1': -1, 'attr2': 50, 'attr3': 1, 'attr4': 20})
(False, '"((attr1>25 and attr2<50) or (attr3=10 and attr4=20))"', {'attrXYZ': 3})
(False, '"((attr1>25 and attr2<50) or (attr3=10 and attr4=20))"', {'attrXYZ': 10})
(False, '"((attr1>25 and attr2<50) or (attr3=10 and attr4=20))"', {'attr1': 20})
(False, '"(2<attrXYZ<10)"', {'attr1': 25, 'attr2': 8, 'attr3': 123})
(False, '"(2<attrXYZ<10)"', {'attr1': 1, 'attr2': 8, 'attr3': 123})
(False, '"(2<attrXYZ<10)"', {'attr1': 26, 'attr2': 8, 'attr3': 123, 'attr4': 1})
(False, '"(2<attrXYZ<10)"', {'attr1': 1, 'attr2': 50, 'attr3': 1, 'attr4': 20})
(False, '"(2<attrXYZ<10)"', {'attr1': -1, 'attr2': 50, 'attr3': 1, 'attr4': 20})
(True, '"(2<attrXYZ<10)"', {'attrXYZ': 3})
(False, '"(2<attrXYZ<10)"', {'attrXYZ': 10})
(False, '"(2<attrXYZ<10)"', {'attr1': 20})
(False, '"(attr1=20 and attr2=20 and attr3=20 and attr4=20)"', {'attr1': 25, 'attr2': 8, 'attr3': 123})
(False, '"(attr1=20 and attr2=20 and attr3=20 and attr4=20)"', {'attr1': 1, 'attr2': 8, 'attr3': 123})
(False, '"(attr1=20 and attr2=20 and attr3=20 and attr4=20)"', {'attr1': 26, 'attr2': 8, 'attr3': 123, 'attr4': 1})
(False, '"(attr1=20 and attr2=20 and attr3=20 and attr4=20)"', {'attr1': 1, 'attr2': 50, 'attr3': 1, 'attr4': 20})
(False, '"(attr1=20 and attr2=20 and attr3=20 and attr4=20)"', {'attr1': -1, 'attr2': 50, 'attr3': 1, 'attr4': 20})
(False, '"(attr1=20 and attr2=20 and attr3=20 and attr4=20)"', {'attrXYZ': 3})
(False, '"(attr1=20 and attr2=20 and attr3=20 and attr4=20)"', {'attrXYZ': 10})
(False, '"(attr1=20 and attr2=20 and attr3=20 and attr4=20)"', {'attr1': 20})
(False, '"(attr1=20 or (attr2=20 and attr3=20 and attr4=20 and attr1231231=1))"', {'attr1': 25, 'attr2': 8, 'attr3': 123})
(False, '"(attr1=20 or (attr2=20 and attr3=20 and attr4=20 and attr1231231=1))"', {'attr1': 1, 'attr2': 8, 'attr3': 123})
(False, '"(attr1=20 or (attr2=20 and attr3=20 and attr4=20 and attr1231231=1))"', {'attr1': 26, 'attr2': 8, 'attr3': 123, 'attr4': 1})
(False, '"(attr1=20 or (attr2=20 and attr3=20 and attr4=20 and attr1231231=1))"', {'attr1': 1, 'attr2': 50, 'attr3': 1, 'attr4': 20})
(False, '"(attr1=20 or (attr2=20 and attr3=20 and attr4=20 and attr1231231=1))"', {'attr1': -1, 'attr2': 50, 'attr3': 1, 'attr4': 20})
(False, '"(attr1=20 or (attr2=20 and attr3=20 and attr4=20 and attr1231231=1))"', {'attrXYZ': 3})
(False, '"(attr1=20 or (attr2=20 and attr3=20 and attr4=20 and attr1231231=1))"', {'attrXYZ': 10})
(True, '"(attr1=20 or (attr2=20 and attr3=20 and attr4=20 and attr1231231=1))"', {'attr1': 20})

Answer 2

只有在确定查询字符串是安全的情况下才执行此操作。

（编辑：你真的应该用pyparsing之类的东西，而不是做一些又快又脏的事情。）

如果源来自不受信任的输入，则不要对查询字符串使用exec。在

import re

QUERY_EXEC_RE = re.compile('(\w+)=')

def _matches(query_exec, d):
    a = []
    exec('a.append({0})'.format(query_exec), globals(), locals())
    return a[0]

def query_dicts(query, dicts):
    query_exec = QUERY_EXEC_RE.sub(r'd.get("\1") == ', query)
    return [d for d in dicts if _matches(query_exec, d)]

示例：

^{pr2}$