Why Python, Ruby, and Javascript are slow

Alex GaynorWaza 2013

You may know me from...

rdio.com

• CPython

• Django

• PyPy

Twitter rants about how computers are bad

Topaztopazruby.com

There is no benchmark but your benchmark

Lame Excuses about why they’re Slow

Dynamic Typing

“You can monkey patch anything”

Harder to Optimizevs.

Slow

The Truth

Let’s talk about C

struct Point { double x; double y; double z;};

class Point(object): def __init__(self, x, y, z): self.x = x self.y = y self.z = z

data = { "x" x, "y": y, "z": z,}

Dictionaryvs.

Object

std::hash_set<std::string, double> point;point["x"] = x;point["y"] = y;point["z"] = z;

And it would be slow

Why don’t people care?

Let’s talk about strings

Given a string matching: “\w+-\d+”

return the integral part of the value

int(s.split("-", 1)[1])

atoi(strchr(s, '-') + 1)

Things that take time

• Hash table lookups

• Allocations

• Copying

The C way:

BYOB

char *data = malloc(1024);while (true) { read(fd, data, 1024); char *start = data; while (start < data + 1024) { if (isspace(*start)) { break; } start++; } printf("%s\n", start);}

while True: data = os.read(fd, 1024) print data.lstrip()

long *squares(long n) { long *sq = malloc(sizeof(long) * n); for (long i = 0; i < n; i++) { sq[i] = i * i; } return sq;}

def squares(n): sq = [] for i in xrange(n): sq.append(i * i) return sq

Missing APIs

from __pypy__ import newlist_hintdef squares(n): sq = newlist_hint(n) for i in xrange(n): sq.append(i * i) return sq

Don’t make us add heuristics

Heuristics = WAG

Growing divide between optimizing and

not

Recap

• Line for line these languages are fast!

• Take care in data structures (data structure heuristics are the WORST)

• We need better no-copy/preallocate APIs

Don’t abandon beauty, simplicity, our values for

performance

Make performance beautiful.

Thank you!https://speakerdeck.com/alex

@alex_gaynor

If there’s time

• Java collections vs. Array and Hash. Need more choices.

• Stop writing C extensions, use something like cffi

• Teach good benchmarking practices