Python code reading (chapter 35): fully (deeply) expand nested lists

Python Code reading collection Introduction ： Why not recommend Python Beginners directly look at the project source code

The code read in this article realizes the complete expansion of all nesting levels of a nested list , The function of forming a simple list .

The code snippet read in this article comes from 30-seconds-of-python.

deep_flatten

from collections.abc import Iterable

def deep_flatten(lst): 
  return [a for i in lst for a in deep_flatten(i)] if isinstance(lst, Iterable) else [lst]

# EXAMPLES
deep_flatten([1, [2], [[3], 4], 5]) # [1,2,3,4,5]
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deep_flatten The function receives a nested list , Return to the fully expanded list . Function USES isinstance() And collections.abc.Iterable To check whether an element is iteratable （ Is it list）. If it is , Recursively call... In the list derivation deep_flatten() function , Otherwise return to [lst].

Primitive function ：

def deep_flatten(lst): 
  return [a for i in lst for a in deep_flatten(i)] if isinstance(lst, Iterable) else [lst]
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It can be rewritten as ：

def deep_flatten(lst): 
  if isinstance(lst, Iterable):
    return [a for i in lst for a in deep_flatten(i)]
  else:
    return [lst]
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Function judgment if lst If it's an iteratable object , Is executed return [a for i in lst for a in deep_flatten(i)]. At this moment if i Is an iterable object , stay deep_flatten(i) The list derivation will continue to be called in , Continue to expand the nested list ; If i It's not an iterative object , In deep_flatten(i) And you'll come back [i], here a The value is i, In the list derivation, you will get the element of a non iteratable object , Untie the nesting layer on the element .

A step closer , The function can be rewritten as ：

from collections.abc import Iterable

def deep_flatten(lst):
  temp = []
  def f(lst):
    if isinstance(lst, Iterable):
      for i in lst:
        for a in f(i):
          temp.append(a)
      return []
    else:
      return [lst]
  f(lst)
  return temp

print(deep_flatten([1, [2], [[3], 4], 5])) # [1,2,3,4,5]
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