python中关于for循环的实例详解

这篇文章主要介绍了python中关于for循环使用过程中的碎碎念,需要的朋友可以参考下

# 1
with ...:
  for ...:
    if ...:
      try:
      except:
    else: 

result = []
for item in item_list:
  new_item = do_something_with(item)
  result.append(item) 

from functools import reduce
summation = reduce(lambda x, y: x + y, numbers) 

>>> a = list(range(10))
>>> a
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> all(a)
False
>>> any(a)
True
>>> max(a)
9
>>> min(a)
0
>>> list(filter(bool, a))
[1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> set(a)
{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
>>> dict(zip(a,a))
{0: 0, 1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9}
>>> sorted(a, reverse=True)
[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
>>> str(a)
'[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]'
>>> sum(a)
45 

results = []
for item in item_list:
  # setups
  # condition
  # processing
  # calculation
  results.append(result) 

def process_item(item):
  # setups
  # condition
  # processing
  # calculation
  return result

results = [process_item(item) for item in item_list] 

results = []
for i in range(10):
  for j in range(i):
    results.append((i, j)) 

results = [(i, j)
      for i in range(10)
      for j in range(i)] 

# finding the max prior to the current item
a = [3, 4, 6, 2, 1, 9, 0, 7, 5, 8]
results = []
current_max = 0
for i in a:
  current_max = max(i, current_max)
  results.append(current_max)

# results = [3, 4, 6, 6, 6, 9, 9, 9, 9, 9] 

def max_generator(numbers):
  current_max = 0
  for i in numbers:
    current_max = max(i, current_max)
    yield current_max

a = [3, 4, 6, 2, 1, 9, 0, 7, 5, 8]
results = list(max_generator(a)) 

from itertools import accumulate
a = [3, 4, 6, 2, 1, 9, 0, 7, 5, 8]
resutls = list(accumulate(a, max)) 

另外，如果你在迭代组合的序列，还有product()，permutations()，combinations()可以用。

结论

1.大多数情况下是不需要写for循环的。

2.应该避免使用for循环，这样会使得代码有更好的阅读性。

行动

1.再看一遍你的代码，找出任何以前凭直觉写下for循环的地方，再次思考一下，不用for循环再写一遍是不是有意义的。

2.分享你很难不使用for循环的例子。

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