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How can I check whether a variable is defined in Ruby? Is there an isset-type method available?
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To check if a variable is undefined, you can use comparison operators — the equality operator == or strict equality operator === . If you declare a variable but not assign a value, it will return undefined automatically. Thus, if you try to display the value of such variable, the word "undefined" will be displayed.
To check if the variable is defined in a local scope, you can use the locals() function, which returns a dictionary representing the current local symbol table. if 'x' in locals(): print('Variable exist. ')
Finally, the standard way to check for null and undefined is to compare the variable with null or undefined using the equality operator ( == ). This would work since null == undefined is true in JavaScript. That's all about checking if a variable is null or undefined in JavaScript.
Python doesn't have a specific function to test whether a variable is defined, since all variables are expected to have been defined before use, even if initially assigned the None object.
Use the defined? keyword (documentation). It will return a String with the kind of the item, or nil if it doesn’t exist.
>> a = 1 => 1 >> defined? a => "local-variable" >> defined? b => nil >> defined? nil => "nil" >> defined? String => "constant" >> defined? 1 => "expression" As skalee commented: "It is worth noting that variable which is set to nil is initialized."
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