파이썬 이해 및 생성기 표현식

>>> nums = (321, 1, 1, 0, 5.3, 2)

# manual implementation
>>> sqr_nums = []
>>> for n in nums:
...     sqr_nums.append(n * n)
... 
>>> sqr_nums
[103041, 1, 1, 0, 28.09, 4]

# list comprehension
>>> [n * n for n in nums]
[103041, 1, 1, 0, 28.09, 4]

# manual implementation
def remove_dunder(obj):
    names = []
    for n in dir(obj):
        if '__' not in n:
            names.append(n)
    return names

# using 'filter' function
def remove_dunder(obj):
    return list(filter(lambda n: '__' not in n, dir(obj)))

>>> def remove_dunder(obj):
...     return [n for n in dir(obj) if '__' not in n]
... 
>>> remove_dunder(dict)
['clear', 'copy', 'fromkeys', 'get', 'items', 'keys', 'pop',
 'popitem', 'setdefault', 'update', 'values']

>>> p = [1, 3, 5]
>>> q = [3, 214, 53]
>>> [i + j for i, j in zip(p, q)]
[4, 217, 58]
>>> [i * j for i, j in zip(p, q)]
[3, 642, 265]

>>> names = ['Jo', 'Joe', 'Jon']
>>> pairs = []
>>> for i, n1 in enumerate(names):
...     for n2 in names[i+1:]:
...         pairs.append((n1, n2))
... 
>>> pairs
[('Jo', 'Joe'), ('Jo', 'Jon'), ('Joe', 'Jon')]
# note that the loop order is same as the manual implementation
>>> [(n1, n2) for i, n1 in enumerate(names) for n2 in names[i+1:]]
[('Jo', 'Joe'), ('Jo', 'Jon'), ('Joe', 'Jon')]

>>> marks = dict(Rahul=68, Ravi=92, Rohit=75, Rajan=85, Ram=80)
>>> {k: v for k, v in marks.items() if v >= 80}
{'Ravi': 92, 'Rajan': 85, 'Ram': 80}

>>> colors = {'teal', 'blue', 'green', 'yellow', 'red', 'orange'}
>>> {c for c in colors if 'o' in c}
{'yellow', 'orange'}

>>> dishes = ('Poha', 'Aloo tikki', 'Baati', 'Khichdi', 'Makki roti')
>>> tuple(d for d in dishes if len(d) < 6)
('Poha', 'Baati')

An object representing a stream of data. Repeated calls to the iterator’s __next__() method (or passing it to the built-in function next()) return successive items in the stream. When no more data are available a StopIteration exception is raised instead.

>>> filter_obj = filter(lambda n: '__' not in n, dir(tuple))
>>> filter_obj
<filter object at 0x7fd910e2de80>
>>> for x in filter_obj:
...     print(x)
... 
count
index

>>> names = filter(lambda n: '__' not in n, dir(tuple))
>>> next(names)
'count'
>>> next(names)
'index'
>>> next(names)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

>>> nums = [321, 1, 1, 0, 5.3, 2]
>>> iter(nums)
<list_iterator object at 0x7fd90e7f8ee0>

>>> import random 
>>> names = ['Jo', 'Ravi', 'Joe', 'Raj', 'Jon']
>>> random.shuffle(names)
>>> random_name = iter(names)
>>> next(random_name)
'Jon'
>>> next(random_name)
'Ravi'

Each time next() is called on it, the generator resumes where it left off (it remembers all the data values and which statement was last executed).

>>> def fibonacci(n):
...     a, b = 0, 1
...     for _ in range(n):
...         yield a
...         a, b = b, a + b
... 
>>> fibonacci(5)
<generator object fibonacci at 0x7fd90e7b22e0>
>>> list(fibonacci(10))
[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

>>> nums = [100, 53, 32, 0, 11, 5, 2]
>>> (n * n for n in nums)
<generator object <genexpr> at 0x7fd90e7b22e0>
>>> g = (n * n for n in nums)
>>> next(g)
10000

# here's a generator version of the sum_sqr_evens(iterable) function
# note that () is optional here for the generator expression
>>> sum(n * n for n in nums if n % 2 == 0)
11028

# inner product
>>> sum(i * j for i, j in zip((1, 3, 5), (2, 4, 6)))
44

>>> items = (1, 'hi', [10, 20], 'bye')
>>> ':'.join(items)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: sequence item 0: expected str instance, int found
>>> ':'.join(str(i) for i in items)
'1:hi:[10, 20]:bye'

>>> marks = dict(Rahul=86, Ravi=92, Rohit=75, Rajan=79, Ram=92)
>>> sort_by_value(marks)
{'Rohit': 75, 'Rajan': 79, 'Rahul': 86, 'Ravi': 92, 'Ram': 92}

>>> word_slices('i')
['i']
>>> word_slices('to')
['to']
>>> word_slices('table')
['ta', 'tab', 'tabl', 'table', 'ab', 'abl', 'able', 'bl', 'ble', 'le']