CODEWITHSUNDEEP
pythonnamedtuple
Peter Stewart
Peter Stewart

Reputation: 3017

namedtuple._replace() doesn't work as described in the documentation

I was having trouble implementing namedtuple._replace(), so I copied the code right off of the documentation:

Point = namedtuple('Point', 'x,y')

p = Point(x=11, y=22)

p._replace(x=33)

print p

and I got:

Point(x=11, y=22)

instead of:

Point(x=33, y=22)

as is shown in the doc.

I'm using Python 2.6 on Windows 7

What's going on?

Upvotes: 68

Views: 55649

Answers (5)

AVP
AVP

Reputation: 11

But YES, you are right: in the 'official' documentation, they forgot to assign the replaced tuple to a variable: https://docs.python.org/3/library/collections.html?highlight=collections#collections.namedtuple

p._replace(x=33)

instead of

p1 = p._replace(x33)

Upvotes: 1

hughdbrown
hughdbrown

Reputation: 49013

It looks to me as if namedtuple is immutable, like its forebear, tuple.

>>> from collections import namedtuple
>>> Point = namedtuple('Point', 'x,y')
>>>
>>> p = Point(x=11, y=22)
>>>
>>> p._replace(x=33)
Point(x=33, y=22)
>>> print(p)
Point(x=11, y=22)
>>> p = p._replace(x=33)
>>> print(p)
Point(x=33, y=22)

NamedTuple._replace returns a new NamedTuple of the same type but with values changed.

Upvotes: 6

Lasse V. Karlsen
Lasse V. Karlsen

Reputation: 391336

Yes it does, it works exactly as documented.

._replace returns a new namedtuple, it does not modify the original, so you need to write this:

p = p._replace(x=33)

See here: somenamedtuple._replace(kwargs) for more information.

Upvotes: 129

Max Shawabkeh
Max Shawabkeh

Reputation: 38603

A tuple is immutable. _replace() returns a new tuple with your modifications:

p = p._replace(x=33)

Upvotes: 21

Ignacio Vazquez-Abrams
Ignacio Vazquez-Abrams

Reputation: 798606

namedtuple._replace() returns a new tuple; the original is unchanged.

Upvotes: 13

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