Coding style in CPython implementation

[Στέφανος Σωφρονίου]

Greetings everyone.

I have noticed that in many if conditions the following syntax is used:

a) if (variable == NULL) { ... }
b) if (variable == -1) { ... }
c) if (variable != NULL) { ... }

What I wanted to ask is, is there a particular reason for not choosing

a) if (!variable) { ... } in place of if (variable == NULL) { ... },
b) if (-1 == variable) { ... } in place of if (variable == -1) { ... }, and
c) if (variable) { ... } in place of if (variable) { ... } ?

Especially the (b) syntax is extremely dangerous to assign -1 to variable in case of an accidental mistyping of equals sign; it had happened countless times by now to to many of us that use various C-family languages.

Is there a particular reason for using this specific coding style?

Regards,

Stefanos