How to create a numpy array of all True or all False

Question

In Python  how do I create a numpy array of arbitrary shape filled with all True or all False

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If it doesn t have to be writeable you can create such an array with np broadcast to    gt  gt  gt  import numpy as np  gt  gt  gt  np broadcast to True   2  5   array    True   True   True   True   True            True   True   True   True   True    dtype bool    If you need it writable you can also create an empty array and fill it yourself    gt  gt  gt  arr   np empty  2  5   dtype bool   gt  gt  gt  arr fill 1   gt  gt  gt  arr array    True   True   True   True   True            True   True   True   True   True    dtype bool    These approaches are only alternative suggestions  In general you should stick with np full  np zeros or np ones like the other answers suggest

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Quickly ran a timeit to see  if there are any differences between the np full and np ones version   Answer  No  import timeit  n array  n test   1000  10000 setup   f import numpy as np  n    n array     print f np ones   timeit timeit  np ones  n  n   dtype bool    number n test  setup setup  s   print f np full   timeit timeit  np full  n  n   True    number n test  setup setup  s     Result   np ones  0 38416870904620737s np full  0 38430388597771525s    IMPORTANT  Regarding the post about np empty  and I cannot comment  as my reputation is too low     DON T DO THAT  DON T USE np empty to initialize an all-True array  As the array is empty  the memory is not written and there is no guarantee  what your values will be  e g    gt  gt  gt  print np empty  4 4   dtype bool      True  True  True  True     True  True  True  True     True  True  True  True     True  True False False

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gt  gt  gt  a   numpy full  2 4   True  dtype bool   gt  gt  gt  a 1  3  True  gt  gt  gt  a array    True   True   True   True            True   True   True   True    dtype bool    numpy full Size  Scalar Value  Type   There is other arguments as well that can be passed  for documentation on that  check https   docs scipy org doc numpy reference generated numpy full html

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numpy already allows the creation of arrays of all ones or all zeros very easily   e g  numpy ones  2  2   or numpy zeros  2  2    Since True and False are represented in Python as 1 and 0  respectively  we have only to specify this array should be boolean using the optional dtype parameter and we are done   numpy ones  2  2   dtype bool   returns   array    True   True            True   True    dtype bool    UPDATE  30 October 2013  Since numpy version 1 8  we can use full to achieve the same result with syntax that more clearly shows our intent  as fmonegaglia points out    numpy full  2  2   True  dtype bool   UPDATE  16 January 2017  Since at least numpy version 1 12  full automatically casts results to the dtype of the second parameter  so we can just write   numpy full  2  2   True

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numpy full  2 2   True  dtype bool

User · Answer

benchmark for Michael Currie s answer import perfplot  bench x   perfplot bench      n range  range 1  200       setup    lambda n   n  n       kernels            lambda shape  np ones shape  dtype  bool           lambda shape  np full shape  True             labels     ones    full      bench x show

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ones and zeros  which create arrays full of ones and zeros respectively  take an optional dtype parameter    gt  gt  gt  numpy ones  2  2   dtype bool  array    True   True            True   True    dtype bool   gt  gt  gt  numpy zeros  2  2   dtype bool  array   False  False           False  False    dtype bool

[python] How to create a numpy array of all True or all False?

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