lambda ??
Paul Rubin
http
Fri Aug 27 10:21:38 CEST 2004
fuzzyman at gmail.com (Michael Foord) writes:
> It starts by giving some basic examples using lambda. What I'm
> wondering is what's the actual difference between these two forms ?
>
> pr = lambda s:s
> *and*
> def pr(s):
> return s
They're the same.
> Is it just a basic example (and so in this case there is no
> difference).. or am I missing something. (What's the point of an
> 'anonymous' function... if you give a name to it !!).
It's like an anonymous expression. Look at the statement
x = a + b * c
That adds the expression 'a' to the expression 'b * c'. If Python
didn't have anonymous expressions, you'd say something like
temp = b * c
x = a + temp
Anonymous just means you can use it as an intermediate result without
having to give it a name of its own.
Example:
def derivative(f, x): # find approximate value of f'(x)
h = .0001
return (f(x+h) - f(x)) / h
def square(x):
return x*x
print derivative(square, 3) # approximately 6
An anonymous function lets you do the same thing without having to
create a named function (like a temporary variable):
print derivative(lambda x: x*x, 3) # same thing
Using a lot of lambdas can be like using a lot of complicated, deeply
nested arithmetic expressions. You have to exercise some judgement to
keep your code readable. But there's a school of thought that says
lambda is a wart in Python and shouldn't be used. That's as silly as
saying you should never say "a + b * c" and instead name every
subexpression with a temp variable.
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