Convert True False value read from file to boolean

Question

I m reading a True - False value from a file and I need to convert it to boolean  Currently it always converts it to True even if the value is set to False   Here s a MWE of what I m trying to do   with open  file dat   mode  r   as f      for line in f          reader   line split             Convert to boolean  lt -- Not working          flag   bool reader 0    if flag      print  flag    True  else      print  flag    False    The file dat file basically consists of a single string with the value True or False written inside  The arrangement looks very convoluted because this is a minimal example from a much larger code and this is how I read parameters into it   Why is flag always converting to True

User · Answer

The cleanest solution that I ve seen is   from distutils util import strtobool def string to bool string       return bool strtobool str string      Sure  it requires an import  but it has proper error handling and requires very little code to be written  and tested

User · Answer

You can do with json    In  124   import json  In  125   json loads  false   Out 125   False  In  126   json loads  true   Out 126   True

User · Answer

pip install str2bool   gt  gt  gt  from str2bool import str2bool  gt  gt  gt  str2bool  Yes   True  gt  gt  gt  str2bool  FaLsE   False

User · Answer

bool  True   and bool  False   always return True because strings  True  and  False  are not empty   To quote a great man  and Python documentation       5 1  Truth Value Testing      Any object can be tested for truth value  for use in an if or while   condition  or as operand of the Boolean operations below  The   following values are considered false           hellip    zero of any numeric type  for example  0  0L  0 0  0j    any empty sequence  for example                 hellip          All other values are considered true  mdash  so objects of many types   are always true    The built-in bool function uses the standard truth testing procedure  That s why you re always getting True   To convert a string to boolean you need to do something like this   def str to bool s       if s     True            return True     elif s     False            return False     else           raise ValueError   evil ValueError that doesn t tell you what the wrong value was

User · Answer

You can use dict to convert string to boolean  Change this line flag   bool reader 0   to   flag     True   True   False   False  get reader 0   False    default is False

User · Answer

If you want to be case-insensitive  you can just do   b   True if bool str lower       true  else False   Example usage    gt  gt  gt  bool str    False   gt  gt  gt  b   True if bool str lower       true  else False  gt  gt  gt  b False  gt  gt  gt  bool str    true   gt  gt  gt  b   True if bool str lower       true  else False  gt  gt  gt  b True

User · Answer

Currently  it is evaluating to True because the variable has a value  There is a good example found here of what happens when you evaluate arbitrary types as a boolean   In short  what you want to do is isolate the  True  or  False  string and run eval on it    gt  gt  gt  eval  True   True  gt  gt  gt  eval  False   False

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Just to add that if your truth value can vary  for instance if it is an input from different programming languages or from different types  a more robust method would be   flag   value in   True   true  1  T   t   1     this can be as long as you want to support   And a more performant variant would be  set lookup is O 1     TRUTHS   set   True   true  1  T   t   1    flag   value in truths

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Use ast literal eval    gt  gt  gt  import ast  gt  gt  gt  ast literal eval  True   True  gt  gt  gt  ast literal eval  False   False      Why is flag always converting to True    Non-empty strings are always True in Python   Related  Truth Value Testing    If NumPy is an option  then    gt  gt  gt  import StringIO  gt  gt  gt  import numpy as np  gt  gt  gt  s    True - False - True   gt  gt  gt  c   StringIO StringIO s   gt  gt  gt  np genfromtxt c  delimiter  -   autostrip True  dtype None   or dtype bool array   True  False   True   dtype bool

User · Answer

I m not suggested this as the best answer  just an alternative but you can also do something like   flag   reader 0      True    flag will be True id reader 0  is  True   otherwise it will be False

User · Answer

If your data is from json  you can do that     import json      json loads  true        True

User · Answer

If you need quick way to convert strings into bools  that functions with most strings  try   def conv2bool arg      try       res   arg 0  upper        T     except Exception e       res  False    return res   or do some more processing with arg if res is false

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Using dicts to convert  quot True quot  in True  def str to bool s  str       status     quot True quot   True                   quot False quot   False      try          return status s      except KeyError as e           logging

User · Answer

you can use distutils util strtobool   gt  gt  gt  from distutils util import strtobool   gt  gt  gt  strtobool  True   1  gt  gt  gt  strtobool  False   0   True values are y  yes  t  true  on and 1  False values are n  no  f  false  off and 0  Raises ValueError if val is anything else

[python] Convert True/False value read from file to boolean

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