List Comprenhensions — 9:41 min

  • 9:41 min | Última modificación: Octubre 5, 2021

[1]:

#
# Llenado de una lista con append
#
squares = []
for x in range(10):
    squares.append(x ** 2)

squares

[1]:

[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

[2]:

#
# Comprenhension equivalente
#
squares = [x ** 2 for x in range(10)]
squares

[2]:

[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

[3]:

#
# Código equivalente usando map()
#
squares = list(map(lambda x: x ** 2, range(10)))
squares

[3]:

[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

[4]:

#
# Creación de pares usando ciclos for anidados
#
combs = []
for x in [1, 2, 3]:
    for y in [3, 1, 4]:
        if x != y:
            combs.append((x, y))

combs

[4]:

[(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]

[5]:

#
# Código equivalente usando un comprenhension
#
[(x, y) for x in [1, 2, 3] for y in [3, 1, 4] if x != y]

[5]:

[(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]

[6]:

#
# Creación de una lista de listas
#
[list(range(5)) for _ in range(5)]

[6]:

[[0, 1, 2, 3, 4],
 [0, 1, 2, 3, 4],
 [0, 1, 2, 3, 4],
 [0, 1, 2, 3, 4],
 [0, 1, 2, 3, 4]]

[7]:

#
# iteracción sobre strings -- MAL
#
nums = ""
for n in range(20):
    nums += str(n)
print(nums)

012345678910111213141516171819

[8]:

#
# Iteración sobre strings -- BIEN
#
nums = []
for n in range(20):
    nums.append(str(n))
print("".join(nums))

012345678910111213141516171819

[9]:

#
# iteración sobre strings -- MEJOR
#
nums = [str(n) for n in range(20)]
"".join(nums)

[9]:

'012345678910111213141516171819'

[10]:

#
# Condicionales. if-then
#
[x for x in range(10) if x < 5]

[10]:

[0, 1, 2, 3, 4]

[11]:

#
# Condicionales. if-else
#
[x if x < 5 else 0 for x in range(10)]

[11]:

[0, 1, 2, 3, 4, 0, 0, 0, 0, 0]

[12]:

#
# Dict comprenhension
#
{letter: i_letter for i_letter, letter in enumerate(["A", "B", "C", "D"])}

[12]:

{'A': 0, 'B': 1, 'C': 2, 'D': 3}

[13]:

#
# Construcción de un generador usando una comprenhension
# =============================================================================
# Numeros del 1 al 20 que contienen un '1'
#
import re

[str(x) for x in range(1, 21) if re.search("1", str(x))]

[13]:

['1', '10', '11', '12', '13', '14', '15', '16', '17', '18', '19']

[14]:

generador = (i ** 2 for i in range(10))
for element in generador:
    print(element)

0
1
4
9
16
25
36
49
64
81

[15]:

generador = (i ** 2 for i in range(10))
display(
    next(generador),
    next(generador),
)

0

1

[16]:

#
# Uso de generadores en funciones
# =============================================================================
#
def num_sequence(n):
    counter = 0
    while counter < n:
        yield counter
        counter += 1


for value in num_sequence(5):
    print(value)

0
1
2
3
4

[17]:

#
# Uso de generadores para leer datos
# =============================================================================
#
data_url = "https://raw.githubusercontent.com/jdvelasq/datalabs/master/datasets/world_bank_development_Indicators.csv"
!wget --quiet {data_url} -P /tmp/


def read_large_file(file_object):

    while True:

        data = file_object.readline()

        if not data:
            break

        yield data


with open("/tmp/world_bank_development_Indicators.csv", "r") as file:

    gen_file = read_large_file(file)

    print(next(gen_file), end="")
    print(next(gen_file), end="")
    print(next(gen_file), end="")

CountryName,CountryCode,Year,Total Population,Urban population (% of total)
Arab World,ARB,1960,92495902.0,31.285384211605397
Caribbean small states,CSS,1960,4190810.0,31.5974898513652