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```from heapq import nlargest as _nlargest, nsmallest as _nsmallest
from __builtin__ import min as _min, max as _max
from itertools import tee, izip, imap, count
from operator import itemgetter

__all__ = ['nsmallest', 'nlargest', 'min', 'max']

def nsmallest(n, iterable, key=None):
"""Find the n smallest elements in a dataset.

Equivalent to:  sorted(iterable, key=key)[:n]
"""
if key is None:
return _nsmallest(n, iterable)
in1, in2 = tee(iterable)
it = izip(imap(key, in1), count(), in2)                 # decorate
result = _nsmallest(n, it)
return map(itemgetter(2), result)                       # undecorate

def nlargest(n, iterable, key=None):
"""Find the n largest elements in a dataset.

Equivalent to:  sorted(iterable, key=key, reverse=True)[:n]
"""
if key is None:
return _nlargest(n, iterable)
in1, in2 = tee(iterable)
it = izip(imap(key, in1), count(), in2)                 # decorate
result = _nlargest(n, it)
return map(itemgetter(2), result)                       # undecorate

def min(iterable, key=None):
if key is None:
return _min(iterable)
it = iter(iterable)
try:
min_elem = it.next()
except StopIteration:
raise ValueError('min() arg is an empty sequence')
min_k = key(min_elem)
for elem in it:
k = key(elem)
if k < min_k:
min_elem = elem
min_k = k
return min_elem

def max(iterable, key=None):
if key is None:
return _max(iterable)
it = iter(iterable)
try:
max_elem = it.next()
except StopIteration:
raise ValueError('max() arg is an empty sequence')
max_k = key(max_elem)
for elem in it:
k = key(elem)
if k > max_k:
max_elem = elem
max_k = k
return max_elem
```