Kind: captions
Language: en
this is the walrus operator and this
is the assignment expression that it
enables it's been added as a feature
to python 3.8 after a whole lot of drama
majority of python core developers as
far as i can tell were against it
and the drama and toxicity over it drove
guido van rossum creator of python to
step
down from his leadership role of
benevolent dictator for life
after he accepted the walrus operator as
part of the
pep 572 proposal so what is it
first let's talk about the assignment
statement
the equal sign in python we can thank
fortran for this i think not very good
design decision of using
the equal sign for assignment
so assigning in this case 42 to the
variable x
most programming languages use it with a
few exceptions pascal uses the walrus
operator
for assignment and r uses a different
operator
this goes against the notation of
mathematics what the equal sign is used
to designate
equality but there's a lesson here i
think that even bad design decisions
once accepted and once we get used to
them
aren't so bad it's all about consistency
so the assignment expression does a
little bit more it also signs
42 to x performs the assignment
operation
but as an expression it returns the
value that it assigned as well
this can be useful in a lot of context
let me talk about the cases where i
find them particularly useful so i use
regular expressions a lot as part of
data science
to clean up and organize data so a
common piece of code you might see is
you perform a
regular expression match returning it to
a variable like res
here that contains the regular
expression object if a match was found
and contains none if no match was found
and then you have some kind of
conditional like an if statement that
checks whether a match was found
and if it has been found then you do
something with the regular expression
object
in python 3.8 all that gets combined
into a single line
that performs the match operation
assigns the result of the match to res
and then check if rest contains a
regular expression object a similar use
case is
in reading files there's a lot of ways
to read a file but a lower level version
there's usually a while loop then
there's a read operation that's stored
in the chunk variable or something like
that
and then there's a condition that checks
whether chunk contains anything or if
end of file was reached at which point
you break out of the while loop
if it has not been reached then you do
something with the data that was fetched
in python 3.8 this gets compressed into
a single line
that performs the read operation the
assignment of the fetch data to the
variable chunk and then the conditional
check in the while loop
of whether chunk returned any data or if
the end of the file was reached
to me this is elegant other use cases in
list comprehensions you can share sub
expressions like in the filter you can
assign
f of x to y and then reuse that y in the
output of the comprehension
you can also in a list reuse the value
for example if it's expensive to compute
so you can compute f of x once assign it
to y and then reuse y in the rest of the
list definition
as a side note i don't like to use
chained assignments
but chain assignments have the same
feature that
the function f is only computed once so
this particular statement here
is equivalent to computing f1 assigning
it to attempt variable and then
assigning that temp
variable to both x and y there are quite
a few criticisms that are both objective
and subjective
that talk about the complexities of
programming language design
and human nature in general so first is
the idea
that both the equal sign and the walrus
operator perform an assignment so it
might be confusing to beginners
i'm not sure about the history of pep
but my guess is that this criticism was
more prevalent before the exception was
added that assignment expressions can't
be
aligned stand alone by themselves
without using parentheses
i think this clarifies to beginners that
assignment expression should not be used
as an assignment statement there's a set
of principles
defined in pap 20 otherwise called zen
of python
that has some ideas to aspire to in the
design of python
just like guido said some of these are
subjective
and i think they are ideas to aspire to
as opposed to perfectly implement
because they're overlapping and there's
a natural tension between them
so first principle that's been brought
up is there should be only one
obvious way to do it and some people
argue that the walrus operator
performs an operation that already had
another way to do the same exact thing
i've also heard a funny kind of
criticism that the equals operator
worked like an assignment expression in
c and it kind of sucked and see
or at least was error prone so there you
go you have a
case study in the real world where this
kind of operator being used to designate
an assignment expression was
error prone another then a python
principle that people brought up
is that simple is better than complex
and
while it seems that the assignment
expression makes the code
simpler in fact it was argued that it
was only reducing white space and was in
fact adding complexity or at least
moving the complexity finally the
criticism that applies
often in programming language design is
that not enough testing was done on how
actual developers will use it
i think that's probably the biggest
challenge of programming language design
and design in general is you don't know
how people how thousands or millions of
developers are going to use this feature
once it's in the wild
and how other features will interact
with it when it's in the wild
so this criticism is certainly true but
i think it is always true
my own feelings about the walrus
operator is i think when used properly
it's quite elegant and even beautiful
but it also represents more than that to
me it represents the importance of
leadership in a community of smart
people that disagree
so this is the feature that led guido to
resign
and i spoke with him on the podcast that
i host and i'll speak to him again
i think he's one of the most brilliant
language designers and programmers we
have
also a great leader in the software
engineer community so this is a little
excerpt from a post he made
it reads now that pep 572 is done
i don't ever want to have to fight so
hard for a pep and find that so many
people despise my decisions
i would like to remove myself entirely
from the decision process
i'm basically giving myself a permanent
vacation from being bdfl
and you all will be on your own so what
are you all going to do
create a democracy anarchy a
dictatorship
a federation so to me the walrus
operator represents more than just
assignment expressions it
represents the power of leadership to uh
break through a toxic stalemate i think
leaders have to make difficult decisions
sometimes
unpopular decisions and sometimes
ones if you look at the long arc of
history prove out to be
bad decisions but without leadership i
think we can't make progress so
the messiness the chaos of democracy
is that the divisiveness can be
paralyzing
and we need leaders to inspire us to
guide us
and to make difficult risky decisions
so to me the walrus operator be useful
for regular expressions
but it will also be a reminder of the
importance of leadership
in the programming world and in our
world in general
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