Python List Comprehensions All In One

Python List Comprehensions All In One

列表推导式

print([i for i in range(10)])
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

print([i for i in range(20) if i%2 == 0])
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

nums = [1, 2, 3, 4]
arr = [i for i in range(len(nums))]
print("arr =", arr)
[0, 1, 2, 3]

nums = [1, 2, 3, 4]
fruit = ["Apples", "Peaches", "Pears", "Bananas"]

print([(i, f) for i in nums for f in fruit])
[(1, 'Apples'), (1, 'Peaches'), (1, 'Pears'), (1, 'Bananas'),
 (2, 'Apples'), (2, 'Peaches'), (2, 'Pears'), (2, 'Bananas'),
 (3, 'Apples'), (3, 'Peaches'), (3, 'Pears'), (3, 'Bananas'),
 (4, 'Apples'), (4, 'Peaches'), (4, 'Pears'), (4, 'Bananas')]

BDFL Pronouncements

The syntax proposed above is the Right One.
The form [x, y for ...] is disallowed; ❌
one is required to write [(x, y) for ...] ✅
The form [... for x... for y...] nests, with the last index varying fastest, just like nested for loops. 🚀

https://peps.python.org/pep-0202/

List displays

list_display ::=  "[" [starred_list | comprehension] "]"

https://docs.python.org/3/reference/expressions.html#list-displays

REPL

https://www.runoob.com/try/runcode.php?filename=HelloWorld&type=python3

demos

list, enumerate, range, lambda, for...loop

#!/usr/bin/env python3
# coding: utf8

__author__ = 'xgqfrms'
__editor__ = 'vscode'
__version__ = '1.0.1'
__github__ = 'https://github.com/xgqfrms/Raspberry-Pi'
__git__ = 'https://github.com/xgqfrms/Raspberry-Pi.git'
__copyright__ = """
  Copyright (c) 2012-2050, xgqfrms; mailto:xgqfrms@xgqfrms.xyz
"""

"""

/**
 * 
 * @author xgqfrms
 * @license MIT
 * @copyright xgqfrms
 * @created 2020-01-01
 * @updated 2023-07-01
 * 
 * @description 
 * @augments 
 * @example 
 * @link 
 * 
 */

"""


# ✅ List types
from typing import List

# class Solution:
#   def runningSum(self, nums: List[int]) -> List[int]:
#     result = []
#     print("len(result)", len(result))
#     # print("len(result)", len(result), result[0])
#     # for i, item in enumerate(nums):
#     #   temp = item
#     #   # ❌ IndexError: list index out of range
#     #   print("len(result)", len(result), result, i)
#     #   if(len(result) > 0):
#     #     print("✅", result[i])
#     #     temp += result[i]
#     #   # result[i] = temp
#     #   result.append(temp)
#     return result

#  🚀
# class Solution:
#   def runningSum(self, nums: List[int]) -> List[int]:
#     for i, item in enumerate(nums):
#       if(i > 0):
#         nums[i] += nums[i - 1]
#     return nums
#  🚀
class Solution:
  def runningSum(self, nums: List[int]) -> List[int]:
    for i in range(1,len(nums)):
      nums[i] += nums[i - 1]
    return nums

# ✅
# class Solution:
#   def runningSum(self, nums: List[int]) -> List[int]:
#     for i in range(len(nums)):
#       if(i > 0):
#         nums[i] += nums[i - 1]
#     return nums

# ✅
# class Solution:
#   def runningSum(self, nums: List[int]) -> List[int]:
#     temp = 0
#     result = []
#     for item in nums:
#       temp += item
#       result.append(temp)
#     return result

# ✅
# class Solution:
#   def runningSum(self, nums: List[int]) -> List[int]:
#     result = []
#     for i, item in enumerate(nums):
#       result.append(item)
#       for j in range(len(result) - 1):
#         result[i] += nums[j]
#     return result

# test cases
t1 = [1,2,3,4]
t2 = [1,1,1,1,1]
t3 = [3,1,2,10,1]
tests = [t1, t2, t3]

r1 = [1,3,6,10]
r2= [1,2,3,4,5]
r3 = [3,4,6,16,17]
results = [r1, r2, r3]


def test():
  solution = Solution()
  for index, test in enumerate(tests):
    value = solution.runningSum(test)
    result = results[index]
    if(str(value) == str(result)):
      print("✅ passed", index)
    else:
      print("❌ failed", value, result)



if __name__ == '__main__':
  print('main / init 👻')

try:
  test()
except KeyboardInterrupt:
  print('Ctrl + C exit ✅')
except RuntimeError as error:
  print('error =', error, error.args[0])
  pass
except Exception as error:
  print('exception =', error)
  raise error
finally:
  # cleanup
  print('finally, clear buffer! 👻')
# print('exit Python REPL')
exit()

'''
# $ python3 ./1480_running-sum-of-1d-array.py
$ py3 ./1480_running-sum-of-1d-array.py

main / init 👻
✅ passed 0
✅ passed 1
✅ passed 2
finally, clear buffer! 👻


https://leetcode.com/problems/running-sum-of-1d-array/description/


'''

#  🚀
# class Solution:
#   def runningSum(self, nums: List[int]) -> List[int]:
#     for i, item in enumerate(nums):
#       if(i > 0):
#         nums[i] += nums[i - 1]
#     return nums

#  🚀
class Solution:
  def runningSum(self, nums: List[int]) -> List[int]:
    for i in range(1,len(nums)):
      nums[i] += nums[i - 1]
    return nums

# ✅
# class Solution:
#   def runningSum(self, nums: List[int]) -> List[int]:
#     for i in range(len(nums)):
#       if(i > 0):
#         nums[i] += nums[i - 1]
#     return nums

# ✅
# class Solution:
#   def runningSum(self, nums: List[int]) -> List[int]:
#     temp = 0
#     result = []
#     for item in nums:
#       temp += item
#       result.append(temp)
#     return result

# ✅
# class Solution:
#   def runningSum(self, nums: List[int]) -> List[int]:
#     result = []
#     for i, item in enumerate(nums):
#       result.append(item)
#       for j in range(len(result) - 1):
#         result[i] += nums[j]
#     return result

https://leetcode.com/problems/running-sum-of-1d-array/submissions/

#!/usr/bin/python3

nums = [1,2,3,4,5]
arr = [x for x in nums[1:]]
print("arr =", arr)

for j in nums[1:]:
  print("j =", j)

""" 
$ py3 ./list-for-loop.py

arr = [2, 3, 4, 5]
j = 2
j = 3
j = 4
j = 5

"""

python dynamic create list

python create list with for loop one line

https://stackoverflow.com/questions/1545050/python-one-line-for-expression

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