How to initialize a dict with keys from a list and empty value in Python

Question

I d like to get from this   keys    1 2 3    to this    1  None  2  None  3  None    Is there a pythonic way of doing it   This is an ugly way to do it    gt  gt  gt  keys    1 2 3   gt  gt  gt  dict   1 2     1  2   gt  gt  gt  dict zip keys   None  len keys     1  None  2  None  3  None

User · Answer

In many workflows where you want to attach a default   initial value for arbitrary keys  you don t need to hash each key individually ahead of time  You can use collections defaultdict  For example   from collections import defaultdict  d   defaultdict lambda  None   print d 1      None print d 2      None print d 3      None   This is more efficient  it saves having to hash all your keys at instantiation  Moreover  defaultdict is a subclass of dict  so there s usually no need to convert back to a regular dictionary   For workflows where you require controls on permissible keys  you can use dict fromkeys as per the accepted answer   d   dict fromkeys  1  2  3  4

User · Answer

dict fromkeys  1  2  3  4    This is actually a classmethod  so it works for dict-subclasses  like collections defaultdict  as well  The optional second argument specifies the value to use for the keys  defaults to None

User · Answer

gt  gt  gt  keyDict     a   b   c   d     gt  gt  gt  dict   key      for key in keyDict     Output     a        c        b        d

User · Answer

default keys    1   quot name quot    To get dictionary with None as values  dict fromkeys default keys     Output    1  None   name   None   To get dictionary with default values  dict fromkeys default keys         Output    1       name

User · Answer

You could use dict fromkeys as follows  dict fromkeys  1  2  3  4   list     This will create a list object for each key  If you change value for any specific key it won t affect other keys  as most people would want  I presume

User · Answer

d      for i in keys      d i    None

User · Answer

nobody cared to give a dict-comprehension solution     gt  gt  gt  keys    1 2 3 5 6 7   gt  gt  gt   key  None for key in keys   1  None  2  None  3  None  5  None  6  None  7  None

User · Answer

dict fromkeys keys  None

[dictionary] How to initialize a dict with keys from a list and empty value in Python?

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