Converting from a string to boolean in Python

Question

Does anyone know how to do convert from a string to a boolean in Python  I found this link  But it doesn t look like a proper way to do it   I e  using built-in functionality  etc   The reason I m asking this is because I learned about int  string   from here  But when trying bool  string   it always returns True    gt  gt  gt  bool  False   True

User · Answer

Starting with Python 2 6  there is now ast literal eval        import ast     help ast literal eval  Help on function literal eval in module ast   literal eval node or string      Safely evaluate an expression node or a string containing a Python     expression   The string or node provided may only consist of the following     Python literal structures  strings  numbers  tuples  lists  dicts  booleans      and None    Which seems to work  as long as you re sure your strings are going to be either  True  or  False         ast literal eval  True   True     ast literal eval  False   False     ast literal eval  F   Traceback  most recent call last     File     line 1  in    File   opt Python-2 6 1 lib python2 6 ast py   line 68  in literal eval     return  convert node or string    File   opt Python-2 6 1 lib python2 6 ast py   line 67  in  convert     raise ValueError  malformed string   ValueError  malformed string     ast literal eval   False     False    I wouldn t normally recommend this  but it is completely built-in and could be the right thing depending on your requirements

User · Answer

This version keeps the semantics of constructors like int value  and provides an easy way to define acceptable string values   def to bool value       valid     true   True   t   True   1   True                false   False   f   False   0   False                         if isinstance value  bool           return value      if not isinstance value  basestring           raise ValueError  invalid literal for boolean  Not a string         lower value   value lower       if lower value in valid          return valid lower value      else          raise ValueError  invalid literal for boolean    s     value      Test cases assert to bool  true      true  is True   assert to bool  True      True  is True   assert to bool  TRue      TRue  is True   assert to bool  TRUE      TRUE  is True   assert to bool  T      T  is True   assert to bool  t      t  is True   assert to bool  1      1  is True   assert to bool True    True is True   assert to bool u true     unicode  true  is True   assert to bool  false   is False    false  is False   assert to bool  False   is False    False  is False   assert to bool  FAlse   is False    FAlse  is False   assert to bool  FALSE   is False    FALSE  is False   assert to bool  F   is False    F  is False   assert to bool  f   is False    f  is False   assert to bool  0   is False    0  is False   assert to bool False  is False   False is False  assert to bool u false   is False   unicode  false  is False     Expect ValueError to be raised for invalid parameter    try      to bool         to bool 12      to bool         to bool  yes       to bool  FOObar   except ValueError  e      pass

User · Answer

If you know the string will be either  True  or  False   you could just use eval s     gt  gt  gt  eval  True   True  gt  gt  gt  eval  False   False   Only use this if you are sure of the contents of the string though  as it will throw an exception if the string does not contain valid Python  and will also execute code contained in the string

User · Answer

A cool  simple trick  based on what  Alan Marchiori posted   but using yaml   import yaml  parsed   yaml load  true   print bool parsed    If this is too wide  it can be refined by testing the type result  If the yaml-returned type is a str  then it can t be cast to any other type  that I can think of anyway   so you could handle that separately  or just let it be true   I won t make any guesses at speed  but since I am working with yaml data under Qt gui anyway  this has a nice symmetry

User · Answer

If you like me just need boolean from variable which is string  You can use distils as mentioned earlier by  jzwiener  However I could not import and use the module as he suggested   Instead I end up using it this way on python3 7    from distutils import util   to handle str to bool conversion enable deletion    False  enable deletion   bool util strtobool enable deletion     distutils is part of the python std lib so no need of installation  Which is great

User · Answer

A dict  really  a defaultdict  gives you a pretty easy way to do this trick   from collections import defaultdict bool mapping   defaultdict bool    Will give you False for non-found values for val in   True    yes             bool mapping val    True  print bool mapping  True      True print bool mapping  kitten      False   It s really easy to tailor this method to the exact conversion behavior you want -- you can fill it with allowed Truthy and Falsy values and let it raise an exception  or return None  when a value isn t found  or default to True  or default to False  or whatever you want

User · Answer

I just had to do this    so maybe late to the party - but someone may find it useful  def str to bool input  default                 Default   not default str   input     result       T           false            true      T       T           false            false     F       F           true             true      T       F           true             false     F              if default          not default str    false      else          not default str    true       if input lower      not default str          return not default     else          return default

User · Answer

I realize this is an old post  but some of the solutions require quite a bit of code  here s what I ended up using   def str2bool value       return   True   True   true   True  get value  False

User · Answer

UPDATE NOTE  DON T EVER USE eval   IF it takes an input directly from the user because it is highly subject to abuse  eval  os system    rm -rf         But cheers  Study finds also that eval   is not evil and it is perfectly OK for TRUSTED CODE  You can use it to convert a boolean string such as  quot False quot  and  quot True quot  to a boolean type   I would like to share my simple solution  use the eval    It will convert the string True and False to proper boolean type IF the string is exactly in title format True or False always first letter capital or else the function will raise an error  e g   gt  gt  gt  eval  False   False   gt  gt  gt  eval  True   True  Of course for dynamic variable you can simple use the  title   to format the boolean string   gt  gt  gt  x    true   gt  gt  gt  eval x title    True  This will throw an error   gt  gt  gt  eval  true   Traceback  most recent call last     File  quot  lt stdin gt  quot   line 1  in  lt module gt    File  quot  lt string gt  quot   line 1  in  lt module gt  NameError  name  true  is not defined   gt  gt  gt  eval  false   Traceback  most recent call last     File  quot  lt stdin gt  quot   line 1  in  lt module gt    File  quot  lt string gt  quot   line 1  in  lt module gt  NameError  name  false  is not defined

User · Answer

Really  you just compare the string to whatever you expect to accept as representing true  so you can do this   s     True    Or to checks against a whole bunch of values   s lower   in   true    1    t    y    yes    yeah    yup    certainly    uh-huh     Be cautious when using the following    gt  gt  gt  bool  foo   True  gt  gt  gt  bool     False   Empty strings evaluate to False  but everything else evaluates to True  So this should not be used for any kind of parsing purposes

User · Answer

def str2bool str     if isinstance str  basestring  and str lower   in   0   false   no        return False   else      return bool str    idea  check if you want the string to be evaluated to False  otherwise bool   returns True for any non-empty string

User · Answer

The usual rule for casting to a bool is that a few special literals  False  0  0 0              are false and then everything else is true  so I recommend the following   def boolify val       if  isinstance val  basestring  and bool val            return not val in   False    0    0 0       else          return bool val

User · Answer

This is the version I wrote  Combines several of the other solutions into one   def to bool value               Converts  something  to boolean  Raises exception if it gets a string it doesn t handle      Case is ignored for strings  These string values are handled        True   True    1    TRue    yes    y    t        False       0    faLse    no    n    f      Non-string values are passed to bool              if type value     type              if value lower   in   yes    y    true     t    1                return True         if value lower   in   no     n    false    f    0                    return False         raise Exception  Invalid value for boolean conversion      value      return bool value    If it gets a string it expects specific values  otherwise raises an Exception  If it doesn t get a string  just lets the bool constructor figure it out  Tested these cases   test cases           true   True         t   True         yes   True         y   True         1   True         false   False         f   False         no   False         n   False         0   False            False        1  True        0  False        1 0  True        0 0  False            False            False            False         1   True         1 2   True         1    True        None  False        object    True

User · Answer

you could always do something like   myString    false  val    myString     true     the bit in parens would evaluate to False  This is just another way to do it without having to do an actual function call

User · Answer

If you have control over the entity that s returning true false  one option is to have it return 1 0 instead of true false  then  boolean response   bool int response   The extra cast to int handles responses from a network  which are always string  Update 2021   quot which are always string quot  -- this is a naive observation  It depends on the serialization protocol used by the library  Default serialization of high-level libraries  the ones used by most web devs  is typically to convert to string before being serialized to bytes  And then on the other side   it s deserialized from bytes to string  so you ve lost any type information

User · Answer

def str2bool v     return v lower   in   yes    true    t    1     Then call it like so    gt  gt  gt  str2bool  yes   True  gt  gt  gt  str2bool  no   False  gt  gt  gt  str2bool  stuff   False  gt  gt  gt  str2bool  1   True  gt  gt  gt  str2bool  0   False     Handling true and false explicitly   You could also make your function explicitly check against a True list of words and a False list of words   Then if it is in neither list  you could throw an exception

User · Answer

Here s is my version  It checks against both positive and negative values lists  raising an exception for unknown values  And it does not receive a string  but any type should do   def to bool value                  Converts  something  to boolean  Raises exception for invalid formats            Possible True  values  1  True   1    TRue    yes    y    t             Possible False values  0  False  None               0    faLse    no    n    f   0 0                  if str value  lower   in   yes    y    true     t    1    return True     if str value  lower   in   no     n    false    f    0    0 0        none                return False     raise Exception  Invalid value for boolean conversion      str value     Sample runs    gt  gt  gt  to bool True  True  gt  gt  gt  to bool  tRUe   True  gt  gt  gt  to bool  1   True  gt  gt  gt  to bool 1  True  gt  gt  gt  to bool 2  Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   lt stdin gt    line 9  in to bool Exception  Invalid value for boolean conversion  2  gt  gt  gt  to bool     False  gt  gt  gt  to bool     False  gt  gt  gt  to bool None  False  gt  gt  gt  to bool  Wasssaaaaa   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   lt stdin gt    line 9  in to bool Exception  Invalid value for boolean conversion  Wasssaaaaa  gt  gt  gt

User · Answer

I like to use the ternary operator for this  since it s a bit more succinct for something that feels like it shouldn t be more than 1 line   True if myString   True  else False

User · Answer

I use    function def toBool x       return x in   True   true  True     test cases   x  toBool x   for x in  True  True   true  False  False   false  None 1 0 -1 123       Result    True  True      True   True      true   True     False  False      False   False      false   False     None  False     1  True     0  False     -1  False     123  False

User · Answer

By using Python s built-in eval   function and the  capitalize   method  you can convert any  true      false  string  regardless of initial capitalization  to a true Python boolean     For example   true false    trUE  type true false     OUTPUT   lt type  str  gt   true false   eval true false capitalize    type true false     OUTPUT   lt type  bool  gt

User · Answer

Yet another option from ansible module utils parsing convert bool import boolean boolean  no     False boolean  yEs     True boolean  true     True

User · Answer

If you know that your input will be either  True  or  False  then why not use   def bool convert s       return s     True

User · Answer

The JSON parser is also useful for in general converting strings to reasonable python types    gt  gt  gt  import json  gt  gt  gt  json loads  false  lower    False  gt  gt  gt  json loads  True  lower    True

User · Answer

Here s something I threw together to evaluate the truthiness of a string   def as bool val    if val    try     if not int val   val False   except  pass   try     if val lower     false   val False   except  pass  return bool val    more-or-less same results as using eval but safer

User · Answer

Use package str2bool pip install str2bool

User · Answer

here s a hairy  built in way to get many of the same answers   Note that although python considers    to be false and all other strings to be true  TCL has a very different idea about things      gt  gt  gt  import Tkinter  gt  gt  gt  tk   Tkinter Tk    gt  gt  gt  var   Tkinter BooleanVar tk   gt  gt  gt  var set  false    gt  gt  gt  var get   False  gt  gt  gt  var set  1    gt  gt  gt  var get   True  gt  gt  gt  var set   exec  rm -r        gt  gt  gt  var get   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   usr lib python2 5 lib-tk Tkinter py   line 324  in get     return self  tk getboolean self  tk globalgetvar self  name    tkinter TclError  0expected boolean value but got   exec  rm -r       gt  gt  gt     A good thing about this is that it is fairly forgiving about the values you can use   It s lazy about turning strings into values  and it s hygenic about what it accepts and rejects notice that if the above statement were given at a tcl prompt  it would erase the users hard disk      the bad thing is that it requires that Tkinter be available  which is usually  but not universally true  and more significantly  requires that a Tk instance be created  which is comparatively heavy     What is considered true or false depends on the behavior of the Tcl GetBoolean  which considers 0  false  no and off to be false and 1  true  yes and on to be true  case insensitive   Any other string  including the empty string  cause an exception

User · Answer

I don t agree with any solution here  as they are too permissive  This is not normally what you want when parsing a string   So here the solution I m using   def to bool bool str          Parse the string and return the boolean value encoded or raise an exception        if isinstance bool str  basestring  and bool str           if bool str lower   in   true    t    1    return True         elif bool str lower   in   false    f    0    return False       if here we couldn t parse it     raise ValueError   s is no recognized as a boolean value    bool str    And the results    gt  gt  gt   to bool v  for v in   true   t   1   F   FALSE   0     True  True  True  False  False  False   gt  gt  gt  to bool     Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   lt stdin gt    line 8  in to bool ValueError     is no recognized as a boolean value   Just to be clear because it looks as if my answer offended somebody somehow   The point is that you don t want to test for only one value and assume the other  I don t think you always want to map Absolutely everything to the non parsed value  That produces error prone code   So  if you know what you want code it in

User · Answer

Use   bool distutils util strtobool some string      Python 2  http   docs python org 2 distutils apiref html highlight distutils util distutils util strtobool Python 3  https   docs python org 3 distutils apiref html distutils util strtobool      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    Be aware that distutils util strtobool   returns integer representations and thus it needs to be wrapped with bool   to get Boolean values

User · Answer

You probably already have a solution but for others who are looking for a method to convert a value to a boolean value using  standard  false values including None          and    in addition to false  no   and 0   def toBoolean  val                 Get the boolean value of the provided input           If the value is a boolean return the value          Otherwise check to see if the value is in            false    f    no    n    none    0                            and returns True if value is not in the list              if val is True or val is False          return val      falseItems     false    f    no    n    none    0                         return not str  val   strip   lower   in falseItems

[python] Converting from a string to boolean in Python?

Examples related to python

Examples related to string

Examples related to boolean