[0x2c8]

Can you elaborate on this? What is wrong with Python's `lambda`?

[rustyminnow]

Like others have said:

- Can only have one line

- Can only use expressions, not statements. E.g. `print`s, loops, conditionals are out.

- Overall just kinda clunky

Here's an SO post about lambdas where the answer is "Use def instead." https://stackoverflow.com/questions/14843777/how-to-write-py...

[seertaak]

Exactly. Kind of an own-goal too, from none other than ex-BDFL. While not totally obvious, it's not impossible to widen the syntax to allow multi-line lambdas, you just need to ditch the stack-based lexer-integrated whitespace sensitivity behaviour.

[diarrhea]

This works for conditionals:

    In [4]: f = lambda x: "Yes" if x else "No"

    In [5]: f(True)
    Out[5]: 'Yes'

    In [6]: f(False)
    Out[6]: 'No'

It's Python's version of ternary operators, so not sure if that counts as a "true" conditional; but it is one.

Loops don't work, but list comprehensions do, and they are definitely the way to go here. Multi-line loops deserve a `def`.

[dragonwriter]

> Can only use expressions, not statements. E.g. `print`s, loops, conditionals are out.

print is a function (and thus can be used in expressions)

python has conditional expressions (<true-val> if <cond> else <false-val>)

loops are a limitation, though comprehensions, map(), functools.reduce(), and the itertools module can allow lots of looping functionality in an expression.

[heavyset_go]

print() is a function now and you can use it with lambdas.

[pmiller2]

Even in Python 2, you can do something like this:

    println = lambda s: sys.stdout.write(s + '\n')

Not that it really makes things much better, but, at least it shows you can do it.

[bobbylarrybobby]

The lambda calculus is Turing complete, so in theory, Python’s lambdas should suffice...

[jolux]

Turing completeness is completely unrelated to whether or not anonymous functions are easy to use in Python.

[zelphirkalt]

Which of course says nothing about usability and readability.

[rustyminnow]

I mean... You're right. They suffice. They're just less friendly (i.e. useful) than lambdas in other languages.

[pansa2]

Python’s `lambda` can only contain a single expression.

There’s no good way to add support for full anonymous functions to Python’s grammar. One of the rules that makes significant-whitespace work elegantly is that statements can contain expressions, but never vice-versa.

[omaranto]

Plenty of languages with significant-whitespace have multiline anonymous functions, like Haskell, Standard ML, Ocaml, etc. Maybe it's no possible in Python for a student reason, but the reason is not that the syntax is bad on indentation.

[pansa2]

The syntaxes of those languages are fundamentally different from Python’s. They don’t have an “expressions may not contain statements” rule - they don’t even have statements.

[omaranto]

It sounds like you agree with me: the reason Python does not have multiline lambdas is not that it has significant-whitespace, but other decisions including the “expressions may not contain statements” rule.

[c-cube]

Nitpick : neither ocaml nor SML have significant whitespace.

[omaranto]

You're right! It's been too long since I used them. I think I was probably remembering F#'s light syntax.

[kissgyorgy]

It can only have one line for example.

[Iwan-Zotow]

no, not correct

[ausjke]

since lambda is for simple and short anonymous functions most of the time why do I need type the whole word each time? can they also do what javascript does(or similar):

    x => x * 2

instead of

    lambda x : x * 2

[pansa2]

Until very recently, Python’s grammar was strictly LL(1), so the parser couldn’t handle, for example, `(x, y) => x * y`.

Perhaps with the move to a PEG parser, this syntax could now be supported?

[cabalamat]

I like:

    λx: x*2

[VWWHFSfQ]

The use of lambda is becoming somewhat of a smell in Python in general. PSF's own black code formatter will complain about using it and pretty much always says to just use a def instead