It all started with a tweet

Browsing through Twitter I came across a particular tweet today. It was a simple expression in Python, accompanied by a challenge to guess its evaluated result.

False == False in [False]

Although I didn’t get it at first, after a little bit of strenous staring I decided that it was False, or True I can no longer recall.

The answer is True though. If you’re confused (I’m looking at you, future me) pay attention to the order of precedence.

Led to discord

It was interesting, so I shared the tweet with a discord server of coding comrades. There, the Python specialist of the troupe posed a challenge of their own.

if False == False is [False,True]: print("4")
else: print("5")

While I knew the result was 4, I remarked that it would be syntactically incorrect since the body blocks were not indented (nor line broken).

And I had remarked wrong!

Having dabbled very little with Python, I only knew that indents were strict, not that a single body statement could be written in the same line!

Anoth…er discovery

Also turns out, Python has truthy and falsey values. I for some reason had been thinking it was unique to JavaScript as it was among the first things I learnt.

With some experimentation

if 9: print("it was true ...thy!")
if '.': print("this was also truthy!")
if [1,2,3]: print("trueee")

if 0: print("i am never getting printed")
if '': print("me neither")
if []: print("well will i be printed? no")
it was true ...thy!
this was also truthy!

I found out that the rules are mostly similar to JavaScript, except Python is more sensible in that an empty array evaluates as falsey.

Looking for stricter booleans

But now I cannot remember anywhere else that has strict booleans. C?

Ah, I have already found an answer (the next day). Empty strings '' are also evaluated as true in C. Almost everything except for 0 and (null) has evaluated to true. Although, when I say true, I just mean if’s body was executed since C doesn’t have actual booleans.

In experimenting to find this, I have now understood why schools teach scanf instead of argv. Data types.