Detailed explanation of the built-in function filter in Python

This article mainly introduces python Built-in function filter related information, friends in need can refer to

python built-in function filter

class filter(object):
 """
 filter(function or None, iterable) --> filter object
 
 Return an iterator yielding those items of iterable for which function(item)
 is true. If function is None, return the items that are true.
 """

filter(func, iterator)

func: The value obtained in custom or anonymous function is a Boolean value, true will retain the value obtained by the function The value of false is inverted.
iterator: iterable object.

Example:

Filter list ['text_test_text', 'test_text_1', 'text_test_2', '3_test_text', 'test_test']
As long as it contains textStringand take it out or negate it.

s.rfind'text'+1

rfind() in Python3 returns the position of the last occurrence of the string, if there is no match Returns -1.
0 in numbers is false, and integers above 0 are all true, so there will be +1 after s.rfind'text', no character found and -1+1=0.

# Filter

li = ['text_test_text', 'test_text_1', 'text_test_2', '3_test_text', 'test_test']

# 默认保留函数所取到的值
print(list(filter(lambda s: s.rfind('text') + 1, li)))
# 取反，下三个例子是一样的
print(list(filter(lambda s: not s.rfind('text') + 1, li)))

# Noe Custom function

l1 = ['text_test_text', 'test_text_1', 'text_test_2', '3_test_text', 'test_test']


def distinguish(l):
 nl = []
 for s in l:
  if s.rfind("text") + 1:
   nl.append(s)
 return nl


print(distinguish(l1))

# Two Custom High Order function

l2 = ['text_test_text', 'test_text_1', 'text_test_2', '3_test_text', 'test_test']


def f(s):
 return s.rfind('text') + 1


def distinguish(func, array):
 nl = []
 for s in array:
  if func(s):
   nl.append(s)
 return nl


print(distinguish(f, l2))

# Three anonymous function

l3 = ['text_test_text', 'test_text_1', 'text_test_2', '3_test_text', 'test_test']


def distinguish(func, array):
 nl = []
 for s in array:
  if func(s):
   nl.append(s)
 return nl

print(distinguish(lambda s: s.rfind('text') + 1, l3))

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