Numpy Checking if a value is NaT

Question

nat   np datetime64  NaT   nat    nat  gt  gt  FutureWarning  In the future   NAT    x  and  x    NAT  will always be False   np isnan nat   gt  gt  TypeError  ufunc  isnan  not supported for the input types  and the inputs could not be safely coerced to any supported types according to the casting rule   safe     How can I check if a datetime64 is NaT   I can t seem to dig anything out of the docs   I know Pandas can do it  but I d rather not add a dependency for something so basic

User · Accepted Answer

INTRO  This answer was written in a time when Numpy was version 1 11 and behaviour of NAT comparison was supposed to change since version 1 12  Clearly that wasn t the case and the second part of answer became wrong  The first part of answer may be not applicable for new versions of numpy  Be sure you ve checked MSeifert s answers below   When you make a comparison at the first time  you always have a warning  But meanwhile returned result of comparison is correct   import numpy as np     nat   np datetime64  NaT    def nat check nat       return nat    np datetime64  NaT        nat check nat  Out 4   FutureWarning  In the future   NAT    x  and  x    NAT  will always be False  True  nat check nat  Out 5   True   If you want to suppress the warning you can use the catch warnings context manager   import numpy as np import warnings  nat   np datetime64  NaT    def nat check nat       with warnings catch warnings            warnings simplefilter  ignore           return nat    np datetime64  NaT        nat check nat  Out 5   True    EDIT  For some reason behavior of NAT comparison in Numpy version 1 12 wasn t change  so the next code turned out to be inconsistent   And finally you might check numpy version to handle changed behavior since version 1 12 0   def nat check nat       if  int x  for x in np   version   split       -1    gt   1  11           return nat    nat     with warnings catch warnings            warnings simplefilter  ignore           return nat    np datetime64  NaT      EDIT  As MSeifert mentioned  Numpy contains isnat function since version 1 13

User · Answer

This approach avoids the warnings while preserving the array-oriented evaluation    import numpy as np def isnat x                datetime64 analog to isnan      doesn t yet exist in numpy - other ways give warnings     and are likely to change                return x astype  i8      np datetime64  NaT   astype  i8

User · Answer

Another way would be to catch the exeption   def is nat npdatetime       try          npdatetime strftime   x           return False     except          return True

User · Answer

Since NumPy version 1 13 it contains an isnat function    gt  gt  gt  import numpy as np  gt  gt  gt  np isnat np datetime64  nat    True   It also works for arrays    gt  gt  gt  np isnat np array   nat   1  2  3  4   nat   5   dtype  datetime64 D     array   True  False  False  False  False   True  False   dtype bool

User · Answer

pandas can check for NaT with pandas isnull    gt  gt  gt  import numpy as np  gt  gt  gt  import pandas as pd  gt  gt  gt  pd isnull np datetime64  NaT    True   If you don t want to use pandas you can also define your own function  parts are taken from the pandas source    nat as integer   np datetime64  NAT   view  i8    def isnat your datetime       dtype string   str your datetime dtype      if  datetime64  in dtype string or  timedelta64  in dtype string          return your datetime view  i8      nat as integer     return False    it can t be a NaT if it s not a dateime   This correctly identifies NaT values    gt  gt  gt  isnat np datetime64  NAT    True   gt  gt  gt  isnat np timedelta64  NAT    True   And realizes if it s not a datetime or timedelta    gt  gt  gt  isnat np timedelta64  NAT   view  i8    False     In the future there might be an isnat-function in the numpy code  at least they have a  currently open  pull request about it  Link to the PR  NumPy github

User · Answer

Very simple and surprisingly fast   without numpy or pandas       str  myDate       NaT               True if myDate is NaT   Ok  it s a little nasty  but given the ambiguity surrounding  NaT  it does the job nicely   It s also useful when comparing two dates either of which might be NaT as follows      str  date1      str  date1           True    str  date1      str  NaT             False    str  NaT        str  date1           False  wait for it        str  NaT        str  Nat             True     hooray

[python] Numpy: Checking if a value is NaT

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