CODEWITHSUNDEEP
pythonboolean
Manu
Manu

Reputation: 77

How to evaluate python string boolean expression using eval()?

I get boolean expression like below :

string = '!True && !(True || False || True)'

I know eval('1+2') returns 3. But when I am executing eval(string) it is throwing me error as in invalid syntax.

Is there any other way I can execute the above expression?

Upvotes: 2

Views: 18785

Answers (3)

alelom
alelom

Reputation: 3008

I recently discovered this package: boolean_parser.

It builds on top of pyparsing, the library that someone else suggested in the answers here.

As its documentation mentions, it has built-in support for this kind of operations:

res = parser.parse('2525 redwood street and 34 blue avenue')
# >> The street_name is: redwood
# >> The street_name is: blue

print(res)

# >> and_(<Street (2525 redwood street)>, <Street (34 blue avenue)>)

Upvotes: 0

syntonym
syntonym

Reputation: 7384

If you want to parse boolean logic (in contrast to control flow) take a look at this stackoverflow post. It mentions pyparsing

The pyparsing module is an alternative approach to creating and executing simple grammars

and sympy.

The logic module for SymPy allows to form and manipulate logic expressions using symbolic and boolean value.

There also seems to be a parser implemented with pyparsing.

Of course you could also write a parser yourself.

Upvotes: 2

Martijn Pieters
Martijn Pieters

Reputation: 1123870

None of !, && and || are valid Python operators; eval() can only handle valid Python expressions.

You'd have to replace those expressions with valid Python versions; presumably ! is not, && is and, and || is or, so you could just replace those with the Python versions:

eval(string.replace('&&', 'and').replace('||', 'or').replace('!', 'not '))

Note the space after not because Python requires this.

The better approach would be to not use the wrong spelling for those operators (they look like Java or JavaScript or C).

Upvotes: 5

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