What are named tuples in Python

Question

Reading the changes in Python 3 1  I found something    unexpected      The sys version info tuple is now a named tuple    I never heard about named tuples before  and I thought elements could either be indexed by numbers  like in tuples and lists  or by keys  like in dicts   I never expected they could be indexed both ways   Thus  my questions are    What are named tuples  How to use them  Why when should I use named tuples instead of normal tuples  Why when should I use normal tuples instead of named tuples  Is there any kind of  named list   a mutable version of the named tuple

User · Answer

namedtuples are a great feature  they are perfect container for data  When you have to  store  data you would use tuples or dictionaries  like   user   dict name  John   age 20    or   user     John   20    The dictionary approach is overwhelming  since dict are mutable and slower than tuples  On the other hand  the tuples are immutable and lightweight but lack readability for a great number of entries in the data fields   namedtuples are the perfect compromise for the two approaches  the have great readability  lightweightness and immutability  plus they are polymorphic

User · Answer

What are named tuples    A named tuple is a tuple   It does everything a tuple can   But it s more than just a tuple    It s a specific subclass of a tuple that is programmatically created to your specification  with named fields and a fixed length    This  for example  creates a subclass of tuple  and aside from being of fixed length  in this case  three   it can be used everywhere a tuple is used without breaking  This is known as Liskov substitutability   New in Python 3 6  we can use a class definition with typing NamedTuple to create a namedtuple   from typing import NamedTuple  class ANamedTuple NamedTuple          a docstring        foo  int     bar  str     baz  list   The above is the same as the below  except the above additionally has type annotations and a docstring  The below is available in Python 2     gt  gt  gt  from collections import namedtuple  gt  gt  gt  class name    ANamedTuple   gt  gt  gt  fields    foo bar baz   gt  gt  gt  ANamedTuple   namedtuple class name  fields    This instantiates it    gt  gt  gt  ant   ANamedTuple 1   bar         We can inspect it and use its attributes    gt  gt  gt  ant ANamedTuple foo 1  bar  bar   baz      gt  gt  gt  ant foo 1  gt  gt  gt  ant bar  bar   gt  gt  gt  ant baz append  anything    gt  gt  gt  ant baz   anything     Deeper explanation  To understand named tuples  you first need to know what a tuple is  A tuple is essentially an immutable  can t be changed in-place in memory  list   Here s how you might use a regular tuple    gt  gt  gt  student tuple    Lisa    Simpson    A   gt  gt  gt  student tuple   Lisa    Simpson    A    gt  gt  gt  student tuple 0   Lisa   gt  gt  gt  student tuple 1   Simpson   gt  gt  gt  student tuple 2   A    You can expand a tuple with iterable unpacking    gt  gt  gt  first  last  grade   student tuple  gt  gt  gt  first  Lisa   gt  gt  gt  last  Simpson   gt  gt  gt  grade  A    Named tuples are tuples that allow their elements to be accessed by name instead of just index    You make a namedtuple like this    gt  gt  gt  from collections import namedtuple  gt  gt  gt  Student   namedtuple  Student     first    last    grade      You can also use a single string with the names separated by spaces  a slightly more readable use of the API    gt  gt  gt  Student   namedtuple  Student    first last grade        How to use them    You can do everything tuples can do  see above  as well as do the following    gt  gt  gt  named student tuple   Student  Lisa    Simpson    A    gt  gt  gt  named student tuple first  Lisa   gt  gt  gt  named student tuple last  Simpson   gt  gt  gt  named student tuple grade  A   gt  gt  gt  named student tuple  asdict   OrderedDict    first    Lisa      last    Simpson      grade    A      gt  gt  gt  vars named student tuple  OrderedDict    first    Lisa      last    Simpson      grade    A      gt  gt  gt  new named student tuple   named student tuple  replace first  Bart   grade  C    gt  gt  gt  new named student tuple Student first  Bart   last  Simpson   grade  C     A commenter asked      In a large script or programme  where does one usually define a named tuple    The types you create with namedtuple are basically classes you can create with easy shorthand  Treat them like classes  Define them on the module level  so that pickle and other users can find them   The working example  on the global module level    gt  gt  gt  from collections import namedtuple  gt  gt  gt  NT   namedtuple  NT    foo bar    gt  gt  gt  nt   NT  foo    bar    gt  gt  gt  import pickle  gt  gt  gt  pickle loads pickle dumps nt   NT foo  foo   bar  bar     And this demonstrates the failure to lookup the definition    gt  gt  gt  def foo            LocalNT   namedtuple  LocalNT    foo bar           return LocalNT  foo    bar         gt  gt  gt  pickle loads pickle dumps foo     Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt   pickle PicklingError  Can t pickle  lt class    main   LocalNT  gt   attribute lookup LocalNT on   main   failed      Why when should I use named tuples instead of normal tuples    Use them when it improves your code to have the semantics of tuple elements expressed in your code    You can use them instead of an object if you would otherwise use an object with unchanging data attributes and no functionality    You can also subclass them to add functionality  for example   class Point namedtuple  Point    x y            adding functionality to a named tuple              slots                 property         def hypot self               return  self x    2   self y    2     0 5         def   str   self               return  Point  x  6 3f  y  6 3f  hypot  6 3f     self x  self y  self hypot       Why when should I use normal tuples instead of named tuples    It would probably be a regression to switch from using named tuples to tuples  The upfront design decision centers around whether the cost from the extra code involved is worth the improved readability when the tuple is used    There is no extra memory used by named tuples versus tuples       Is there any kind of  named list   a mutable version of the named tuple     You re looking for either a slotted object that implements all of the functionality of a statically sized list or a subclassed list that works like a named tuple  and that somehow blocks the list from changing in size     A now expanded  and perhaps even Liskov substitutable  example of the first   from collections import Sequence  class MutableTuple Sequence           Abstract Base Class for objects that work like mutable     namedtuples  Subclass and define your named fields with        slots   and away you go                slots            def   init   self   args           for slot  arg in zip self   slots    args               setattr self  slot  arg      def   repr   self           return type self    name     repr tuple self         more direct   iter   than Sequence s     def   iter   self            for name in self   slots                yield getattr self  name        Sequence requires   getitem    amp    len        def   getitem   self  index           return getattr self  self   slots   index       def   len   self           return len self   slots      And to use  just subclass and define   slots     class Student MutableTuple         slots      first    last    grade    customize     gt  gt  gt  student   Student  Lisa    Simpson    A    gt  gt  gt  student Student  Lisa    Simpson    A    gt  gt  gt  first  last  grade   student  gt  gt  gt  first  Lisa   gt  gt  gt  last  Simpson   gt  gt  gt  grade  A   gt  gt  gt  student 0   Lisa   gt  gt  gt  student 2   A   gt  gt  gt  len student  3  gt  gt  gt   Lisa  in student True  gt  gt  gt   Bart  in student False  gt  gt  gt  student first    Bart   gt  gt  gt  for i in student  print i       Bart Simpson A

User · Answer

Named tuples are basically easy-to-create  lightweight object types   Named tuple instances can be referenced using object-like variable dereferencing or the standard tuple syntax   They can be used similarly to struct or other common record types  except that they are immutable   They were added in Python 2 6 and Python 3 0  although there is a recipe for implementation in Python 2 4   For example  it is common to represent a point as a tuple  x  y    This leads to code like the following   pt1    1 0  5 0  pt2    2 5  1 5   from math import sqrt line length   sqrt  pt1 0 -pt2 0    2    pt1 1 -pt2 1    2    Using a named tuple it becomes more readable   from collections import namedtuple Point   namedtuple  Point    x y   pt1   Point 1 0  5 0  pt2   Point 2 5  1 5   from math import sqrt line length   sqrt  pt1 x-pt2 x   2    pt1 y-pt2 y   2    However  named tuples are still backwards compatible with normal tuples  so the following will still work   Point   namedtuple  Point    x y   pt1   Point 1 0  5 0  pt2   Point 2 5  1 5   from math import sqrt   use index referencing line length   sqrt  pt1 0 -pt2 0    2    pt1 1 -pt2 1    2     use tuple unpacking x1  y1   pt1   Thus  you should use named tuples instead of tuples anywhere you think object notation will make your code more pythonic and more easily readable   I personally have started using them to represent very simple value types  particularly when passing them as parameters to functions   It makes the functions more readable  without seeing the context of the tuple packing   Furthermore  you can also replace ordinary immutable classes that have no functions  only fields with them   You can even use your named tuple types as base classes   class Point namedtuple  Point    x y                 However  as with tuples  attributes in named tuples are immutable    gt  gt  gt  Point   namedtuple  Point    x y    gt  gt  gt  pt1   Point 1 0  5 0   gt  gt  gt  pt1 x   2 0 AttributeError  can t set attribute   If you want to be able change the values  you need another type   There is a handy recipe for mutable recordtypes which allow you to set new values to attributes    gt  gt  gt  from rcdtype import    gt  gt  gt  Point   recordtype  Point    x y    gt  gt  gt  pt1   Point 1 0  5 0   gt  gt  gt  pt1   Point 1 0  5 0   gt  gt  gt  pt1 x   2 0  gt  gt  gt  print pt1 0       2 0   I am not aware of any form of  named list  that lets you add new fields  however   You may just want to use a dictionary in this situation  Named tuples can be converted to dictionaries using pt1  asdict   which returns   x   1 0   y   5 0  and can be operated upon with all the usual dictionary functions     As already noted  you should check the documentation for more information from which these examples were constructed

User · Answer

namedtuple  is one of the easiest ways to clean up your code and make it more readable  It self-documents what is happening in the tuple  Namedtuples instances are just as memory efficient as regular tuples as they do not have per-instance dictionaries  making them faster than dictionaries    from collections import namedtuple  Color   namedtuple  Color     hue    saturation    luminosity      p   Color 170  0 1  0 6   if p saturation  gt   0 5       print  Whew  that is bright    if p luminosity  gt   0 5       print  Wow  that is light    Without naming each element in the tuple  it would read like this   p    170  0 1  0 6  if p 1   gt   0 5      print  Whew  that is bright   if p 2  gt   0 5     print  Wow  that is light    It is so much harder to understand what is going on in the first example  With a namedtuple  each field has a name  And you access it by name rather than position or index  Instead of p 1   we can call it p saturation  It s easier to understand  And it looks cleaner   Creating an instance of the namedtuple is easier than creating a dictionary     dictionary  gt  gt  gt p   dict hue   170  saturation   0 1  luminosity   0 6   gt  gt  gt p  hue   170   nametuple  gt  gt  gt from collections import namedtuple  gt  gt  gt Color   namedtuple  Color     hue    saturation    luminosity     gt  gt  gt p   Color 170  0 1  0 6   gt  gt  gt p hue 170   When might you use namedtuple   As just stated  the namedtuple makes understanding tuples much easier  So if you need to reference the items in the tuple  then creating them as namedtuples just makes sense  Besides being more lightweight than a dictionary  namedtuple also keeps the order unlike the dictionary  As in the example above  it is simpler to create an instance of namedtuple than dictionary  And referencing the item in the named tuple looks cleaner than a dictionary  p hue rather than p  hue      The syntax  collections namedtuple typename  field names   verbose False    rename False      namedtuple is in the collections library   typename  This is the name of the new tuple subclass  field names  A sequence of names for each field  It can be a sequence as in a list   x    y    z   or string x y z  without commas  just whitespace  or x  y  z  rename  If rename is True  invalid fieldnames are automatically replaced with positional names  For example    abc    def    ghi   abc   is converted to   abc     1    ghi     3    eliminating the keyword  def   since that is a reserved word for defining functions  and the duplicate fieldname  abc   verbose  If verbose is True  the class definition is printed just before being built    You can still access namedtuples by their position  if you so choose  p 1     p saturation  It still unpacks like a regular tuple   Methods  All the regular tuple methods are supported  Ex  min    max    len    in  not in  concatenation      index  slice  etc  And there are a few additional ones for namedtuple  Note  these all start with an underscore   replace   make   asdict    replace Returns a new instance of the named tuple replacing specified fields with new values   The syntax  somenamedtuple  replace kwargs    Example   gt  gt  gt from collections import namedtuple   gt  gt  gt Color   namedtuple  Color     hue    saturation    luminosity     gt  gt  gt p   Color 170  0 1  0 6    gt  gt  gt p  replace hue 87  Color 87  0 1  0 6    gt  gt  gt p  replace hue 87  saturation 0 2  Color 87  0 2  0 6    Notice  The field names are not in quotes  they are keywords here  Remember  Tuples are immutable - even if they are namedtuples and have the  replace method  The  replace produces a new instance  it does not modify the original or replace the old value  You can of course save the new result to the variable  p   p  replace hue 169    make  Makes a new instance from an existing sequence or iterable   The syntax  somenamedtuple  make iterable    Example    gt  gt  gt data    170  0 1  0 6    gt  gt  gt Color  make data  Color hue 170  saturation 0 1  luminosity 0 6    gt  gt  gt Color  make  170  0 1  0 6     the list is an iterable Color hue 170  saturation 0 1  luminosity 0 6    gt  gt  gt Color  make  170  0 1  0 6     the tuple is an iterable Color hue 170  saturation 0 1  luminosity 0 6    gt  gt  gt Color  make 170  0 1  0 6   Traceback  most recent call last       File   lt stdin gt    line 1  in  lt module gt      File   lt string gt    line 15  in  make TypeError   float  object is not callable   What happened with the last one  The item inside the parenthesis should be the iterable  So a list or tuple inside the parenthesis works  but the sequence of values without enclosing as an iterable returns an error    asdict  Returns a new OrderedDict which maps field names to their corresponding values   The syntax  somenamedtuple  asdict     Example    gt  gt  gt p  asdict   OrderedDict    hue   169     saturation   0 1     luminosity   0 6      Reference  https   www reddit com r Python comments 38ee9d intro to namedtuple   There is also named list which is similar to named tuple but mutable https   pypi python org pypi namedlist

User · Answer

In Python inside there is a good use of container called a named tuple  it can be used to create a definition of class and has all the features of the original tuple   Using named tuple will be directly applied to the default class template to generate a simple class  this method allows a lot of code to improve readability and it is also very convenient when defining a class

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namedtuple is a factory function for making a tuple class  With that class we can create tuples that are callable by name also  import collections   Create a namedtuple class with names  quot a quot   quot b quot   quot c quot  Row   collections namedtuple  quot Row quot     quot a quot    quot b quot    quot c quot        row   Row a 1 b 2 c 3   Make a namedtuple from the Row class we created  print row     Prints  Row a 1  b 2  c 3  print row a   Prints  1 print row 0   Prints  1  row   Row  make  2  3  4    Make a namedtuple from a list of values  print row    Prints  Row a 2  b 3  c 4

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Another way  a new way  to use named tuple is using NamedTuple from typing package  Type hints in namedtuple Let s use the example of the top answer in this post to see how to use it   1  Before using the named tuple  the code is like this  pt1    1 0  5 0  pt2    2 5  1 5   from math import sqrt  line length   sqrt  pt1 0  - pt2 0    2    pt1 1  - pt2 1    2  print line length    2  Now we use the named tuple from typing import NamedTuple  inherit the NamedTuple class and define the variable name in the new class  test is the name of the class  class test NamedTuple       x  float     y  float  create instances from the class and assign values to them pt1   test 1 0  5 0      x is 1 0  and y is 5 0  The order matters pt2   test 2 5  1 5   use the variables from the instances to calculate line length   sqrt  pt1 x - pt2 x   2    pt1 y - pt2 y   2  print line length

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Everyone else has already answered it  but I think I still have something else to add   Namedtuple could be intuitively deemed as a shortcut to define a class   See a cumbersome and conventional  way to define a class    class Duck      def   init   self  color  weight           self color   color         self weight   weight red duck   Duck  red    10        In  50   red duck     Out 50    lt   main   Duck at 0x1068e4e10 gt      In  51   red duck color     Out 51    red    As for namedtuple  from collections import namedtuple Duck   namedtuple  Duck     color    weight    red duck   Duck  red    10    In  54   red duck Out 54   Duck color  red   weight  10   In  55   red duck color Out 55    red

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named tuples allow backward compatibility with code that checks for the version like this   gt  gt  gt  sys version info 0 2   3  1    while allowing future code to be more explicit by using this syntax   gt  gt  gt  sys version info major 3  gt  gt  gt  sys version info minor 1

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What is namedtuple    As the name suggests  namedtuple is a tuple with name   In standard tuple  we access the elements using the index  whereas namedtuple allows user to define name for elements   This is very handy especially processing csv  comma separated value  files and working with complex and large dataset  where the code becomes messy with the use of indices  not so pythonic    How to use them     gt  gt  gt from collections import namedtuple  gt  gt  gt saleRecord   namedtuple  saleRecord   shopId saleDate salesAmout totalCustomers    gt  gt  gt   gt  gt  gt   gt  gt  gt  Assign values to a named tuple   gt  gt  gt shop11 saleRecord 11  2015-01-01  2300 150    gt  gt  gt shop12 saleRecord shopId 22 saleDate  2015-01-01  saleAmout 1512 totalCustomers 125    Reading    gt  gt  gt  Reading as a namedtuple  gt  gt  gt print  Shop Id    shop12 shopId  12  gt  gt  gt print  Sale Date   shop12 saleDate  2015-01-01  gt  gt  gt print  Sales Amount    shop12 salesAmount  1512  gt  gt  gt print  Total Customers    shop12 totalCustomers  125   Interesting Scenario in CSV Processing    from csv import reader from collections import namedtuple  saleRecord   namedtuple  saleRecord   shopId saleDate totalSales totalCustomers   fileHandle   open  salesRecord csv   r   csvFieldsList csv reader fileHandle  for fieldsList in csvFieldsList      shopRec   saleRecord  make fieldsList      overAllSales    shopRec totalSales   print  Total Sales of The Retail Chain    overAllSales

User · Answer

Try this   collections namedtuple     Basically  namedtuples are easy to create  lightweight object types   They turn tuples into convenient containers for simple tasks   With namedtuples  you don   t have to use integer indices for accessing members of a tuple   Examples   Code 1    gt  gt  gt  from collections import namedtuple   gt  gt  gt  Point   namedtuple  Point   x y     gt  gt  gt  pt1   Point 1 2    gt  gt  gt  pt2   Point 3 4    gt  gt  gt  dot product     pt1 x   pt2 x      pt1 y   pt2 y     gt  gt  gt  print dot product 11   Code 2    gt  gt  gt  from collections import namedtuple   gt  gt  gt  Car   namedtuple  Car   Price Mileage Colour Class     gt  gt  gt  xyz   Car Price   100000  Mileage   30  Colour    Cyan   Class    Y     gt  gt  gt  print xyz  Car Price 100000  Mileage 30  Colour  Cyan   Class  Y    gt  gt  gt  print xyz Class Y

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I think it s worth adding information about NamedTuples using type hinting    dependencies from typing import NamedTuple  Optional    definition class MyNamedTuple NamedTuple       an attribute  str     my attribute  Optional str    None     next attribute  int   1    instantiation my named tuple   MyNamedTuple  quot abc quot    quot def quot     or more explicitly  other tuple   MyNamedTuple an attribute  quot abc quot   my attribute  quot def quot      access assert  quot abc quot     my named tuple an attribute assert 1    other tuple next attribute

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