The Performance Impact of Using dict() Instead of {} in CPython 2.7

    > [tl;dr] Use {} to create dictionaries, especially if you are pre-populating them, unless the literal syntax does not work for your case.
    [...]
    > ...as a general principle I try to avoid code constructions I know to introduce performance hits.

"Premature optimization is the root of all evil".

    {k: v for k, v in some_iterable}

I would hope that over time insights like this combine with others to create a set of "best practices" across a language. After all, readability is largely tied to convention (multi-line ternary if statements excluded!).

The real benefit of these performance tweaks comes in those people writing libraries. After all, most of the matrix routines we depend on today still tie back to FORTRAN - amazing we are using 40 year old code!

Thanks again.

    I’ve been reviewing lot of code lately for various open 
    source and internal projects written in Python. As part of 
    those reviews, I have noticed what I think is a trend 
    toward using dict() instead of {} to create dictionaries. I 
    don’t know exactly why this trend has emerged.

After writing javascript:

var o = { a: 1, b: 2};

... it feels a bit clunky to write Python:

o = { "a": 1, "b": 2}

It does the same thing with [] and list().

I'd rather just use what feels right at the time thanks, PyCharm.