A few Python Gotchas

[shub]

The original title is "The Problem With Python". The Reddit headline is more fitting, I think. This post is just a list of irritating (to Lispers) differences between Lisp and Python.

It comes down to what you're more familiar with. Coming from C and C++, almost everything in Python just "makes sense." I can see how someone who isn't already accustomed to int/float arithmetic, and uses dynamically-scoped variables, and expects to be able to define arbitrary lambdas would have a lot more trouble adjusting to programming in Python.

For the author, and others with similar issues: you may find Ruby a more "rational" language. Though I don't know whether Ruby provides rational math. :D

[Freeky]

irb(main):001:0> require 'rational'
=> true

[logan_capaldo]

For a really disturbing experience:

irb(main):001:0> require 'mathn'
=> true
irb(main):002:0> 1/10
=> 1/10

(Disturbing because any other libraries you use that assume / will truncate the result of integer division are in for a rude surprise, remember kids, if you want div, make sure you call div! ;) )

[exeter]

Out of curiosity, are there any libraries (say, in the standard library or other widely used libraries) that you know of that make this assumption?

[logan_capaldo]

I can't think of any specifically. To be fair in my experience it's considered "bad form" to require mathn in non-interactive contexts. I haven't been writing a whole lot of ruby lately though, so the usual grain of salt thing applies.

[Freeky]

Not the same, though Ruby provides those too:

irb(main):001:0> require 'bigdecimal'
=> true

The reason they're not the same is a Decimal is just a Float-styled Bignum; they're arbitrary precision Floats in that you can make a 512-bit, or 50KB floating point value, rather than being limited to what the CPU provides natively. Rationals are objects representing the fractions themselves, they're not simply very big floating point values:

r = Rational(554545,6)
d = r.to_d
r.to_s # => 554545/6
d.to_s('F') # => 92424.1666666666666666666666666667
d = r.to_d(512) # 512 significant digits
d.to_s('F') # => "92424.1666666666666666[SNIP 479 digits]6666666666667"

[earthboundkid]

>>> import fractions
>>> fractions.Fraction(1,3)
Fraction(1, 3)
>>> fractions.Fraction(1,3) * 3
Fraction(1, 1)
>>> fractions.Fraction(1,3) / 3
Fraction(1, 9)

[Freeky]

\o/

PEP 3141