6.1. Idiom About

  • Returns iterator

  • Generator-like - behaves similarly, but is not a generator

  • range(start, stop, step)

  • reversed(iterable)

  • enumerate(iterable, start=0)

  • zip(*iterable, strict=False)

  • map(func, iterable)

  • filter(func, iterable)

  • next(iterable)

  • iter(iterable)

  • chain(*iterator)

  • any, all, min, max, sum

  • zip, enumerate, chain

  • map, filter, reduce, starmap, zip_longest

  • range, product, permutations

  • partial

6.1.1. Comprehension

  • all value > 1.0

>>> DATA = [
...     ('sepal_length', 'sepal_width', 'petal_length', 'petal_width', 'species'),
...     (5.8, 2.7, 5.1, 1.9, 'virginica'),
...     (5.1, 3.5, 1.4, 0.2, 'setosa'),
...     (5.7, 2.8, 4.1, 1.3, 'versicolor'),
...     (6.3, 2.9, 5.6, 1.8, 'virginica'),
...     (6.4, 3.2, 4.5, 1.5, 'versicolor'),
...     (4.7, 3.2, 1.3, 0.2, 'setosa'),
...     (7.0, 3.2, 4.7, 1.4, 'versicolor'),
... ]

>>> 
... %%timeit -r 1000 -n 1000
... result = []
... for row in DATA:
...     for value in row:
...         if type(value) in (int,float):
...             result.append(value > 1.0)
... result = all(result)
12.2 µs ± 743 ns per loop (mean ± std. dev. of 1000 runs, 1,000 loops each)

>>> 
... %%timeit -r 1000 -n 1000
... result = True
... for row in DATA:
...     for value in row:
...         if type(value) in (int,float):
...             if value <= 1.0:
...                 result = False
...                 break
...
10.5 µs ± 857 ns per loop (mean ± std. dev. of 1000 runs, 1,000 loops each)

>>> 
... %%timeit -r 1000 -n 1000
... result = all(value > 1.0
...              for row in DATA
...              for value in row
...              if type(value) in (int,float))
...
3.71 µs ± 658 ns per loop (mean ± std. dev. of 1000 runs, 1,000 loops each)

>>> 
... %%timeit -r 1000 -n 1000
... result = all(value > 1.0 for row in DATA for value in row if type(value) in (int,float))
...
3.8 µs ± 801 ns per loop (mean ± std. dev. of 1000 runs, 1,000 loops each)

>>> 
... %%timeit -r 1000 -n 1000
... result = all(y > 1.0 for x in DATA for y in x if type(y) in (int,float))
...
4.13 µs ± 941 ns per loop (mean ± std. dev. of 1000 runs, 1,000 loops each)

6.1.2. Map

>>> from dataclasses import dataclass

>>> DATA = """root:x:0:0:root:/root:/bin/bash
... bin:x:1:1:bin:/bin:/sbin/nologin
... daemon:x:2:2:daemon:/sbin:/sbin/nologin
... adm:x:3:4:adm:/var/adm:/sbin/nologin
... shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
... halt:x:7:0:halt:/sbin:/sbin/halt
... nobody:x:99:99:Nobody:/:/sbin/nologin
... sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
... watney:x:1000:1000:Mark Watney:/home/watney:/bin/bash
... lewis:x:1001:1001:Melissa Lewis:/home/lewis:/bin/bash
... martinez:x:1002:1002:Rick Martinez:/home/martinez:/bin/bash"""

>>> @dataclass
... class SystemAccount:
...     username: str
...     uid: int
>>>
>>> @dataclass
... class UserAccount:
...     username: str
...     uid: int

>>> class Account:
...     def __new__(cls, line):
...         username, _, uid, *_ = line.strip().split(':')
...         uid = int(uid)
...         if uid < 1000:
...             return SystemAccount(username, uid)
...         else:
...             return UserAccount(username, uid)
>>>
>>>
>>> result = map(Account, DATA.splitlines())
>>> list(result)  
[SystemAccount(username='root', uid=0),
 SystemAccount(username='bin', uid=1),
 SystemAccount(username='daemon', uid=2),
 SystemAccount(username='adm', uid=3),
 SystemAccount(username='shutdown', uid=6),
 SystemAccount(username='halt', uid=7),
 SystemAccount(username='nobody', uid=99),
 SystemAccount(username='sshd', uid=74),
 UserAccount(username='watney', uid=1000),
 UserAccount(username='lewis', uid=1001),
 UserAccount(username='martinez', uid=1002)]

>>> def account(line):
...     username, _, uid, *_ = line.strip().split(':')
...     uid = int(uid)
...     if uid < 1000:
...         return SystemAccount(username, uid)
...     else:
...         return UserAccount(username, uid)
>>>
>>> def system(account):
...     return account.uid < 1000
>>>
>>>
>>> all_accounts = map(account, DATA.splitlines())
>>> sys_accounts = filter(system, all_accounts)
>>>
>>> list(sys_accounts)  
[SystemAccount(username='root', uid=0),
 SystemAccount(username='bin', uid=1),
 SystemAccount(username='daemon', uid=2),
 SystemAccount(username='adm', uid=3),
 SystemAccount(username='shutdown', uid=6),
 SystemAccount(username='halt', uid=7),
 SystemAccount(username='nobody', uid=99),
 SystemAccount(username='sshd', uid=74)]