What is the preferred syntax for initializing a dict curly brace literals or the dict function

Question

I m putting in some effort to learn Python  and I am paying close attention to common coding standards   This may seem like a pointlessly nit-picky question  but I am trying to focus on best-practices as I learn  so I don t have to unlearn any  bad  habits later  I see two common methods for initializing a dict  a          a    value        another    value      b   dict       a  value       another  value      Which is considered to be  quot more pythonic quot    Which do you use  Why

User · Answer

The first version is preferable    It works for all kinds of keys  so you can  for example  say  1   one   2   two    The second variant only works for  some  string keys  Using different kinds of syntax depending on the type of the keys would be an unnecessary inconsistency  It is faster     python -m timeit  dict a  value   another  value    1000000 loops  best of 3  0 79 usec per loop   python -m timeit    a    value   another    value    1000000 loops  best of 3  0 305 usec per loop  If the special syntax for dictionary literals wasn t intended to be used  it probably wouldn t exist

User · Answer

The first  curly braces  Otherwise  you run into consistency issues with keys that have odd characters in them  like       Works fine  a          a    value        b c    value        Eeep  Breaks if trying to be consistent  b   dict       a  value       b c  value

User · Answer

I think the first option is better because you are going to access the values as a  a   or a  another    The keys in your dictionary are strings  and there is no reason to pretend they are not  To me the keyword syntax looks clever at first  but obscure at a second look  This only makes sense to me if you are working with   dict    and the keywords are going to become attributes later  something like that

User · Answer

I almost always use curly-braces  however  in some cases where I m writing tests  I do keyword packing unpacking  and in these cases dict   is much more maintainable  as I don t need to change   a 1  b 2    to    a   1   b   2    It also helps in some circumstances where I think I might want to turn it into a namedtuple or class instance at a later time   In the implementation itself  because of my obsession with optimisation  and when I don t see a particularly huge maintainability benefit  I ll always favour curly-braces   In tests and the implementation  I would never use dict   if there is a chance that the keys added then  or in the future  would either    Not always be a string Not only contain digits  ASCII letters and underscores Start with an integer  dict 1foo 2  raises a SyntaxError

User · Answer

Curly braces  Passing keyword arguments into dict    though it works beautifully in a lot of scenarios  can only initialize a map if the keys are valid Python identifiers  This works  a     import    trade   1  7 8   a   dict   import    trade   1  7 8    This won t work  a   dict import  trade   1 7 8   It will result in the following error      a   dict import  trade   1 7 8                 SyntaxError  invalid syntax

User · Answer

Sometimes dict   is a good choice   a dict zip   Mon   Tue   Wed   Thu   Fri     x for x in range 1  6      mydict dict zip   mon   tue   wed   thu   fri   sat   sun       random randint 0 100  for x in range 0 7

User · Answer

FYI  in case you need to add attributes to your dictionary  things that are attached to the dictionary  but are not one of the keys   then you ll need the second form   In that case  you can initialize your dictionary with keys having arbitrary characters  one at a time  like so       class mydict dict   pass     a   mydict               a  b c      value      a test   False

[python] What is the preferred syntax for initializing a dict: curly brace literals {} or the dict() function?

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