Range in Python (3)

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*Memo:

• My post explains a range (1).
• My post explains a range (2).

A range can be iterated with a for statement as shown below:

for x in range(5):
    print(x)
# 0
# 1
# 2
# 3
# 4

fruits = ["Apple", "Orange", "Banana", "Kiwi", "Lemon", "Mango"]

for i in range(4):
    print(fruits[i])
# Apple
# Orange
# Banana
# kiwi

for i in range(1, 6, 2):
    print(fruits[i])
# Orange
# Kiwi
# Mango

for i in range(5, 0, -2):
    print(fruits[i])
# Mango
# Kiwi
# Orange

A range can be unpacked with an assignment and for statement, function and * but not with ** as shown below:

v1, v2, v3 = range(3)

print(v1, v2, v3)
# 0 1 2

v1, *v2, v3 = range(6)

print(v1, v2, v3)  # 0 [1, 2, 3, 4] 5
print(v1, *v2, v3) # 0 1 2 3 4 5

for v1, v2, v3 in [range(3), range(3, 6)]:
    print(v1, v2, v3)
# 0 1 2
# 3 4 5

for v1, *v2, v3 in [range(6), range(6, 12)]:
    print(v1, v2, v3)
    print(v1, *v2, v3)
# 0 [1, 2, 3, 4] 5
# 0 1 2 3 4 5
# 6 [7, 8, 9, 10] 11
# 6 7 8 9 10 11

print(*range(4), *range(4, 6))
# 0 1 2 3 4 5

print([*range(4), *range(4, 6)])
# [0, 1, 2, 3, 4, 5]

def func(p1='a', p2='b', p3='c', p4='d', p5='e', p6='f'):
    print(p1, p2, p3, p4, p5, p6)

func()
# a b c d e f

func(*range(4), *range(4, 6))
# 0 1 2 3 4 5

def func(p1='a', p2='b', *args):
    print(p1, p2, args)
    print(p1, p2, *args)
    print(p1, p2, ['A', 'B', *args, 'C', 'D'])

func()
# a b ()
# a b Nothing
# a b ['A', 'B', 'C', 'D']

func(*range(4), *range(4, 6))
# 0 1 (2, 3, 4, 5)
# 0 1 2 3 4 5
# 0 1 ['A', 'B', 2, 3, 4, 5, 'C', 'D']

Even a big range doesn't get MemoryError as shown below:

v = range(100000000)

print(v)
# range(0, 100000000)

print(v[0], v[1], v[2])
# 0 1 2

A range can be read by slicing as shown below:

*Memo:

• Slicing can be done with one or more [start:end:step] in the range [start, end):
  • start(Optional-Default:None-Type:int/NoneType):
    • It's a start index(inclusive).
    • If it's None, it's the 1st index.
    • Don't use start=.
  • end(Optional-Default:None-Type:int/NoneType):
    • It's an end index(exclusive).
    • If it's None, it's the range length.
    • Don't use end=.
  • step(Optional-Default:None-Type:int/NoneType):
    • It's the interval of indices.
    • If it's None, it's 1.
    • It cannot be zero.
    • Don't use end=.
  • The [] with at least one : is slicing.
  • start and end can be signed indices(zero and positive and negative indices).
  • Error doesn't occur even if [start, end) is out of the range [The 1st index, The range length).

v1 = range(10)

print(v1)
# range(0, 10)

print(*v1)
print(*v1[:])
print(*v1[::])
print(*v1[None:None:None])
print(*v1[0:11:1])
print(*v1[-100:100:1])
# 0 1 2 3 4 5 6 7 8 9

v2 = v1[2:8]
v2 = v1[-8:-2]

print(v2)
# range(2, 8)

print(*v2)
# 2 3 4 5 6 7

v2 = v1[2:8:2]
v2 = v1[-8:-2:2]

print(v2)
# range(2, 8)

print(*v2)
# 2 4 6

A range cannot be changed by indexing, slicing and a del statement as shown below:

*Memo:

• A del statement cannot remove zero or more numbers from a range by indexing and slicing but can remove one or more variables themselves.

v = range(6)

print(*v)
# 0 1 2 3 4 5

v[1] = 10
v[-5] = 10
v[3:5] = [20, 30]
v[-3:-1] = [20, 30]
v[1], v[3:5] = 10, [20, 30]
v[-5], v[-3:-1] = 10, [20, 30]
# TypeError: 'range' object does not support item assignment

v = range(6)

print(*v)
# 0 1 2 3 4 5

del v[1], v[3:5]
del v[-5], v[-2:5]
# TypeError: 'range' object does not support item deletion

v = range(5)

del v

print(v)
# NameError: name 'v' is not defined

A range can be continuously used through multiple variables as shown below:

v1 = v2 = v3 = range(5)                # Equivalent
                                       # v1 = range(5)
print(v1, *v1) # range(0, 5) 0 1 2 3 4 # v2 = v1
print(v2, *v2) # range(0, 5) 0 1 2 3 4 # v3 = v2
print(v3, *v3) # range(0, 5) 0 1 2 3 4

A range can be shallow-copied (only by slicing) but cannot deep-copied as shown below:

<Shallow copy>:

*Memo:

• v1 and v2 refer to different ranges (only by slicing) and each same element.
• is keyword can check if v1 and v2 refer to the same range and each same element.
• Slicing can shallow-copy the range.
• copy.copy() cannot shallow-copy a range.

v1 = range(5)
v2 = v1[:]

print(v1, *v1) # range(0, 5) 0 1 2 3 4
print(v2, *v2) # range(0, 5) 0 1 2 3 4

print(v1 is v2, v1[2] is v2[2])
# False True

import copy

v1 = range(5)
v2 = copy.copy(v1)

print(v1, *v1) # range(0, 5) 0 1 2 3 4
print(v2, *v2) # range(0, 5) 0 1 2 3 4

print(v1 is v2, v1[2] is v2[2])
# True True

<Deep copy>:

*Memo:

• v1 and v2 refer to the same range and each same element.
• copy.deepcopy() cannot deep-copy and even shallow-copy a range.

import copy

v1 = range(5)
v2 = copy.deepcopy(v1)

print(v1, *v1) # range(0, 5) 0 1 2 3 4
print(v2, *v2) # range(0, 5) 0 1 2 3 4

print(v1 is v2, v1[2] is v2[2])
# True True