![]() So these finer points may not be relevant for you. However if you use them in an if statement the if will also implicitly call bool on the result. Similarly for or but just the other way around: > Test(True) or Test(10) That's because and actually returns the first operand if the first operand evaluates to False and if it evaluates to True then it returns the second operand: > x1 if (x 10) ), which is the comparison operator, and tests whether x is equal to 10 or not. The outline of this tutorial is as follows: First, you’ll get a quick overview of the if statement in its simplest form. It allows for conditional execution of a statement or group of statements based on the value of an expression. TypeError: _bool_ should return bool, returned int In a Python program, the if statement is how you perform this sort of decision-making. Print('_bool_ called on )".format(self=self) To show how this can be customized I use this class which again prints something to track what is happening: class Test(object): This implicit bool call can be used to customize how your classes behave with and, or and not. Customizing the behavior of your own classes In Python you cannot create functions called and or or because these are keywords.Īlso you should never use "evaluate" or if bool(.). Note that this is pseudo-code not Python code. Python not equal operator returns True if two variables are of same type and have different values, if the values are same then it returns False. So in Pseudo-Code(!) the and and or functions work like these: def and(expr1, expr2): The True and False represent what bool(left-hand-side) returns, they don't have to be True or False, they just need to return True or False when bool is called on them (1). Those always evaluate both operands: > res = print_and_return(False) & print_and_return(True) īut if the first operand isn't enough then, of course, the second operator is evaluated: > res = print_and_return(True) and print_and_return(False) In other words, we will use the > operator to decide whether the if statement needs to be executed. This is not the case for the binary operators. Greater Than or Equal To And Conditional Statements in Python We can also use the greater than or equal operator with the conditional if-else statement. > res = print_and_return(False) and print_and_return(True)Īs you can see only one print statement is executed, so Python really didn't even look at the right operand. This is handy to see what is actuallyĮvaluated because of the print statements: > def print_and_return(value): ![]() To show this I use a function that simply takes a value, prints it and returns it again. That means if the first operand already defines the result, then the second operator isn't evaluated at all. The logical operators (like in many other languages) have the advantage that these are short-circuited. Unary arithmetic and bitwise/binary operations and 6.7. There is no bitwise negation in Python (just the bitwise inverse operator ~ - but that is not equivalent to not). ![]()
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