Python: Comparing empty string to False is False, why?

It doesn't make sense for '' and [] to actually equal False, because they are clearly different values: a string and a list. If they both equalled False they would have to be equal to each other*. They are just "falsey", which means they come out as false when they are converted to a boolean.

(* in any sensibly constructed language)

not is an operation that returns a boolean. Which boolean it returns depends on whether the operand is falsey or not. So not x is not equivalent to x==False; it is equivalent to bool(x)==False.

Such a comparison isn't "Pythonic" (i.e. it isn't what an experienced Python programmer would naturally do). The Pythonic way to proceed is to use a value in a Boolean context such as an if statement, and leave the interpreter to apply the bool built-in invisibly to determine a True or False value. That's why people commonly write code such as

if lst:
    print(headers)
    for item in lst:
        print(item.format())
else:
    print(no_data_message)

rather than using the commonly-seen but less Pythonic if len(lst): or the even clumsier but still functionally correct if len(lst) > 0:.

In some respects unfortunately, Python's designer decided that True and False would be instances of the bool type, and that bool would be a subclass of int. As a result of this True compares equal to 1 and False compares equal to 0. Numerical conversion accounts for the floating-point (and, for that matter, complex) result.

But just because a bool(x) == True doesn't mean x == True, any more than bool(x) == False implies x == False. There are many other values that evaluate false, the best-known being

• Numeric zeroes
• None
• The empty string
• Empty containers (list, tuple, dict)

There's no way they can all be equal to each other!

If you want to check the official explanation, just cast your values like this:

print(bool(None) == False)
print(False == False)
print(bool(0) == False)
print(bool(0.0) == False)
print(bool(0j) == False)
print(bool('') == False)
print(bool(()) == False)
print(bool([]) == False)
print(bool({}) == False)

Because int(False) == 0 and int(True) == 1. This is what Python is doing when it tries to evaluate 0 == False.

On the other hand, bool('') == False. The same goes for bool([]) and bool({}).

The fact that x evaluates to True doesn't necessarily mean that x == True.