Is it possible to set a number to NaN or infinity

Question

Is it possible to set an element of an array to NaN in Python   Additionally  is it possible to set a variable to   - infinity  If so  is there any function to check whether a number is infinity or not

User · Answer

Yes  you can use numpy for that   import numpy as np a   arange 3 dtype float   a 0    np nan a 1    np inf a 2    -np inf  a   is now  nan inf -inf   np isnan a 0     True np isinf a 1     True np isinf a 2     True

User · Answer

Cast from string using float      gt  gt  gt  float  NaN   nan  gt  gt  gt  float  Inf   inf  gt  gt  gt  -float  Inf   -inf  gt  gt  gt  float  Inf      float  Inf   True  gt  gt  gt  float  Inf      1 False

User · Answer

Is it possible to set a number to NaN or infinity    Yes  in fact there are several ways  A few work without any imports  while others require import  however for this answer I ll limit the libraries in the overview to standard-library and NumPy  which isn t standard-library but a very common third-party library    The following table summarizes the ways how one can create a not-a-number or a positive or negative infinity float    -------------------------------------------------------------------       result    NaN             Infinity              -Infinity                module                                                                    ---------- -------------- -------------------- --------------------      built-in    float  nan      float  inf            -float  inf                                          float  infinity       -float  infinity                                     float   inf           float  -inf                                          float   infinity      float  -infinity       ---------- -------------- -------------------- --------------------      math        math nan        math inf              -math inf              ---------- -------------- -------------------- --------------------      cmath       cmath nan       cmath inf             -cmath inf             ---------- -------------- -------------------- --------------------      numpy       numpy nan       numpy PINF            numpy NINF                           numpy NaN       numpy inf             -numpy inf                           numpy NAN       numpy infty           -numpy infty                                         numpy Inf             -numpy Inf                                           numpy Infinity        -numpy Infinity        -------------------------------------------------------------------    A couple remarks to the table    The float constructor is actually case-insensitive  so you can also use float  NaN   or float  InFiNiTy     The cmath and numpy constants return plain Python float objects  The numpy NINF is actually the only constant I know of that doesn t require the -  It is possible to create complex NaN and Infinity with complex and cmath    ------------------------------------------------------------------------------------------       result    NaN 0j            0 NaNj             Inf 0j                 0 Infj                     module                                                                                            ---------- ---------------- ----------------- --------------------- ----------------------      built-in    complex  nan      complex  nanj      complex  inf           complex  infj                                                               complex  infinity      complex  infinityj       ---------- ---------------- ----------------- --------------------- ----------------------      cmath       cmath nan          cmath nanj         cmath inf               cmath infj               ------------------------------------------------------------------------------------------    The options with    return a plain float  not a complex       is there any function to check whether a number is infinity or not    Yes there is - in fact there are several functions for NaN  Infinity  and neither Nan nor Inf  However these predefined functions are not built-in  they always require an import    --------------------------------------------------------------          for    NaN            Infinity or       not NaN and                                         -Infinity         not Infinity and         module                                       not -Infinity           ---------- ------------- ---------------- --------------------      math        math isnan     math isinf        math isfinite          ---------- ------------- ---------------- --------------------      cmath       cmath isnan    cmath isinf       cmath isfinite         ---------- ------------- ---------------- --------------------      numpy       numpy isnan    numpy isinf       numpy isfinite         --------------------------------------------------------------    Again a couple of remarks    The cmath and numpy functions also work for complex objects  they will check if either real or imaginary part is NaN or Infinity  The numpy functions also work for numpy arrays and everything that can be converted to one  like lists  tuple  etc   There are also functions that explicitly check for positive and negative infinity in NumPy  numpy isposinf and numpy isneginf  Pandas offers two additional functions to check for NaN  pandas isna and pandas isnull  but not only NaN  it matches also None and NaT  Even though there are no built-in functions  it would be easy to create them yourself  I neglected type checking and documentation here    def isnan value       return value    value    NaN is not equal to anything  not even itself  infinity   float  infinity    def isinf value       return abs value     infinity   def isfinite value       return not  isnan value  or isinf value      To summarize the expected results for these functions  assuming the input is a float     ----------------------------------------------------------------------              input    NaN      Infinity      -Infinity      something else         function                                                                      ---------------- ------- ------------ ------------- ------------------      isnan             True     False         False          False                ---------------- ------- ------------ ------------- ------------------      isinf             False    True          True           False                ---------------- ------- ------------ ------------- ------------------      isfinite          False    False         False          True                 ----------------------------------------------------------------------       Is it possible to set an element of an array to NaN in Python    In a list it s no problem  you can always include NaN  or Infinity  there    gt  gt  gt   math nan  math inf  -math inf  1     python list  nan  inf  -inf  1    However if you want to include it in an array  for example array array or numpy array  then the type of the array must be float or complex because otherwise it will try to downcast it to the arrays type    gt  gt  gt  import numpy as np  gt  gt  gt  float numpy array   np array  0   0   0    dtype float   gt  gt  gt  float numpy array 0    float  nan    gt  gt  gt  float numpy array array  nan   0    0      gt  gt  gt  import array  gt  gt  gt  float array   array array  d    0  0  0    gt  gt  gt  float array 0    float  nan    gt  gt  gt  float array array  d    nan  0 0  0 0     gt  gt  gt  integer numpy array   np array  0  0  0   dtype int   gt  gt  gt  integer numpy array 0    float  nan   ValueError  cannot convert float NaN to integer

User · Answer

When using Python 2 4  try  inf   float  9e999   nan   inf - inf   I am facing the issue when I was porting the simplejson to an embedded device which running the Python 2 4  float  9e999   fixed it  Don t use inf   9e999  you need convert it from string  -inf gives the -Infinity

[python] Is it possible to set a number to NaN or infinity?

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