Comprehension in Python (1)

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*Memo:

• My post explains a set and dictionary(dict) comprehension.
• My post explains a generator comprehension.
• My post explains a list and the list with indexing.
• My post explains a tuple.

A comprehension is the concise expression to create an iterable. There are a list comprehension, tuple comprehension, set comprehension, dictionary(dict) comprehension and generator comprehension:

<List Comprehension>:

1D list:

sample = [0, 1, 2, 3, 4, 5, 6, 7]

v = [x**2 for x in sample]

print(v)
# [0, 1, 4, 9, 16, 25, 36, 49]

The below is without a list comprehension:

sample = [0, 1, 2, 3, 4, 5, 6, 7]

v = []

for x in sample:
    v.append(x**2)

print(v)
# [0, 1, 4, 9, 16, 25, 36, 49]

2D list:

sample = [[0, 1, 2, 3], [4, 5, 6, 7]]

v = [[y**2 for y in x] for x in sample]

print(v)
# [[0, 1, 4, 9], [16, 25, 36, 49]]

The below is without a list comprehension:

sample = [[0, 1, 2, 3], [4, 5, 6, 7]]

v = []

for i, x in enumerate(sample):
    v.append([])
    for y in x:
        v[i].append(y**2)

print(v)
# [[0, 1, 4, 9], [16, 25, 36, 49]]

3D list:

sample = [[[0, 1], [2, 3]], [[4, 5], [6, 7]]]

v = [[[z**2 for z in y] for y in x] for x in sample]

print(v)
# [[[0, 1], [4, 9]], [[16, 25], [36, 49]]]

The below is without a list comprehension:

sample = [[[0, 1], [2, 3]], [[4, 5], [6, 7]]]

v = []

for i, x in enumerate(sample):
    v.append([])
    for j, y in enumerate(x):
        v[i].append([])
        for z in y:
            v[i][j].append(z**2)

print(v)
# [[[0, 1], [4, 9]], [[16, 25], [36, 49]]]

<Tuple Comprehension>:

*tuple() is used for a tuple comprehension because () is already used for a generator comprehension.

1D tuple:

sample = (0, 1, 2, 3, 4, 5, 6, 7)

v = tuple(x**2 for x in sample)

print(v)
# (0, 1, 4, 9, 16, 25, 36, 49)

The below is without a tuple comprehension:

sample = (0, 1, 2, 3, 4, 5, 6, 7)

v = []

for x in sample:
    v.append(x**2)

v = tuple(v)

print(v)
# (0, 1, 4, 9, 16, 25, 36, 49)

2D tuple:

sample = ((0, 1, 2, 3), (4, 5, 6, 7))

v = tuple(tuple(y**2 for y in x) for x in sample)

print(v)
# ((0, 1, 4, 9), (16, 25, 36, 49))

The below is without a tuple comprehension:

sample = ((0, 1, 2, 3), (4, 5, 6, 7))

v = []

for i, x in enumerate(sample):
    v.append([])
    for y in x:
        v[i].append(y**2)
    v[i] = tuple(v[i])

v = tuple(v)

print(v)
# ((0, 1, 4, 9), (16, 25, 36, 49))

3D tuple:

sample = (((0, 1), (2, 3)), ((4, 5), (6, 7)))

v = tuple(tuple(tuple(z**2 for z in y) for y in x) for x in sample)

print(v)
# (((0, 1), (4, 9)), ((16, 25), (36, 49)))

The below is without a tuple comprehension:

sample = (((0, 1), (2, 3)), ((4, 5), (6, 7)))

v = []

for i, x in enumerate(sample):
    v.append([])
    for j, y in enumerate(x):
        v[i].append([])
        for z in y:
            v[i][j].append(z**2)
        v[i][j] = tuple(v[i][j])
    v[i] = tuple(v[i])

v = tuple(v)

print(v)
# (((0, 1), (4, 9)), ((16, 25), (36, 49)))