[pypy-issue] Issue #2186: PyPy vs CPython2 O(N^2) vs O(N) (pypy/pypy)

[Roman Sinayev]

New issue 2186: PyPy vs CPython2 O(N^2) vs O(N)
https://bitbucket.org/pypy/pypy/issues/2186/pypy-vs-cpython2-o-n-2-vs-o-n

Roman Sinayev:

String concatenation seems to involve copying the whole string, while in Python2 people tend to simply add substrings. Example program:

```
import random
import time

def timing(f):
    def wrap(*args):
        time1 = time.time()
        ret = f(*args)
        time2 = time.time()
        print('%s function took %0.3f ms' % (f.__name__, (time2-time1)*1000.0))
        return ret
    return wrap

@timing
def test():
    s = b''
    for i in range(1*1000*1000):
        c = chr(random.randint(1,128))
        s += c
    return s


if __name__=='__main__':
    test()
```