[英]Python: Find-replace on lists
I first want to note that my question is different from what's in this link: finding and replacing elements in a list (python) 我首先要注意,我的问题与此链接的内容不同: 在列表中查找和替换元素(python)
What I want to ask is whether there is some known API or conventional way to achieve such a functionality (If it's not clear, a function/method like my imaginary list_replace()
is what I'm looking for): 我想问的是,是否有某种已知的API或常规方法来实现这种功能(如果不清楚,我list_replace()
是像我想象中的list_replace()
这样的函数/方法):
>>> list = [1, 2, 3]
>>> list_replace(list, 3, [3, 4, 5])
>>> list
[1, 2, 3, 4, 5]
An API with limitation of number of replacements will be better: 受替换次数限制的API会更好:
>>> list = [1, 2, 3, 3, 3]
>>> list_replace(list, 3, [8, 8], 2)
>>> list
[1, 2, 8, 8, 8, 8, 3]
And another optional improvement is that the input to replace will be a list itself, instead of a single value: 另一个可选的改进是要替换的输入将是列表本身,而不是单个值:
>>> list = [1, 2, 3, 3, 3]
>>> list_replace(list, [2, 3], [8, 8], 2)
>>> list
[1, 8, 8, 3, 3]
Is there any API that looks at least similar and performs these operations, or should I write it myself? 是否有看起来至少相似并执行这些操作的API,还是我应该自己编写?
Try; 尝试;
def list_replace(ls, val, l_insert, num = 1):
l_insert_len = len(l_insert)
indx = 0
for i in range(num):
indx = ls.index(val, indx) #it throw value error if it cannot find an index
ls = ls[:indx] + l_insert + ls[(indx + 1):]
indx += l_insert_len
return ls
This function works for both first and second case; 此功能适用于第一种情况和第二种情况;
It wont work with your third requirement 它不能满足您的第三个要求
Demo 演示
>>> list = [1, 2, 3]
>>> list_replace(list, 3, [3, 4, 5])
[1, 2, 3, 4, 5]
>>> list = [1, 2, 3, 3, 3]
>>> list_replace(list, 3, [8, 8], 2)
[1, 2, 8, 8, 8, 8, 3]
Note It returns a new list; 注意它将返回一个新列表; The list passed in will not change. 传入的列表不会更改。
how about this, it work for the 3 requirements 怎么样,它可以满足3个要求
def list_replace(origen,elem,new,cantidad=None):
n=0
resul=list()
len_elem=0
if isinstance(elem,list):
len_elem=len(elem)
for i,x in enumerate(origen):
if x==elem or elem==origen[i:i+len_elem]:
if cantidad and n<cantidad:
resul.extend(new)
n+=1
continue
elif not cantidad:
resul.extend(new)
continue
resul.append(x)
return resul
>>>list_replace([1,2,3,4,5,3,5,33,23,3],3,[42,42])
[1, 2, 42, 42, 4, 5, 42, 42, 5, 33, 23, 42, 42]
>>>list_replace([1,2,3,4,5,3,5,33,23,3],3,[42,42],2)
[1, 2, 42, 42, 4, 5, 42, 42, 5, 33, 23, 3]
>>>list_replace([1,2,3,4,5,3,5,33,23,3],[33,23],[42,42,42],2)
[1, 2, 3, 4, 5, 3, 5, 42, 42, 42, 23, 3]
Given this isn't hard to write, and not a very common use case, I don't think it will be in the standard library. 鉴于这并不难编写,也不是很常见的用例,所以我认为它不会出现在标准库中。 What would it be named, replace_and_flatten
? 它将被命名为replace_and_flatten
? It's quite hard to explain what that does, and justify the inclusion. 很难解释这样做是什么,并证明包含是否合理。
Explicit is also better than implicit, so... 显式也比隐式好,所以...
def replace_and_flatten(lst, searched_item, new_list):
def _replace():
for item in lst:
if item == searched_item:
yield from new_list # element matches, yield all the elements of the new list instead
else:
yield item # element doesn't match, yield it as is
return list(_replace()) # convert the iterable back to a list
I developed my own function, you are welcome to use and to review it. 我开发了自己的功能,欢迎您使用和审查。
Note that in contradiction to the examples in the question - my function creates and returns a new list. 请注意,与问题中的示例相反,我的函数创建并返回了一个新列表。 It does not modify the provided list. 它不修改提供的列表。
Working examples: 工作示例:
list = [1, 2, 3]
l2 = list_replace(list, [3], [3, 4, 5])
print('Changed: {0}'.format(l2))
print('Original: {0}'.format(list))
list = [1, 2, 3, 3, 3]
l2 = list_replace(list, [3], [8, 8], 2)
print('Changed: {0}'.format(l2))
print('Original: {0}'.format(list))
list = [1, 2, 3, 3, 3]
l2 = list_replace(list, [2, 3], [8, 8], 2)
print('Changed: {0}'.format(l2))
print('Original: {0}'.format(list))
I always print also the original list, so you can see that it is not modified: 我也总是打印原始列表,因此您可以看到它没有被修改:
Changed: [1, 2, 3, 4, 5]
Original: [1, 2, 3]
Changed: [1, 2, 8, 8, 8, 8, 3]
Original: [1, 2, 3, 3, 3]
Changed: [1, 8, 8, 3, 3]
Original: [1, 2, 3, 3, 3]
Now, the code (tested with Python 2.7 and with Python 3.4): 现在,代码(经过Python 2.7和Python 3.4测试):
def list_replace(lst, source_sequence, target_sequence, limit=0):
if limit < 0:
raise Exception('A negative replacement limit is not supported')
source_sequence_len = len(source_sequence)
target_sequence_len = len(target_sequence)
original_list_len = len(lst)
if source_sequence_len > original_list_len:
return list(lst)
new_list = []
i = 0
replace_counter = 0
while i < original_list_len:
suffix_is_long_enough = source_sequence_len <= (original_list_len - i)
limit_is_satisfied = (limit == 0 or replace_counter < limit)
if suffix_is_long_enough and limit_is_satisfied:
if lst[i:i + source_sequence_len] == source_sequence:
new_list.extend(target_sequence)
i += source_sequence_len
replace_counter += 1
continue
new_list.append(lst[i])
i += 1
return new_list
I developed a function for you (it works for your 3 requirements): 我为您开发了一个功能(它可以满足您的3个要求):
def list_replace(lst,elem,repl,n=0):
ii=0
if type(repl) is not list:
repl = [repl]
if type(elem) is not list:
elem = [elem]
if type(elem) is list:
length = len(elem)
else:
length = 1
for i in range(len(lst)-(length-1)):
if ii>=n and n!=0:
break
e = lst[i:i+length]
if e==elem:
lst[i:i+length] = repl
if n!=0:
ii+=1
return lst
I've tried with your examples and it works ok. 我已经尝试了您的示例,但效果很好。
Tests made: 进行的测试:
print list_replace([1,2,3], 3, [3, 4, 5])
print list_replace([1, 2, 3, 3, 3], 3, [8, 8], 2)
print list_replace([1, 2, 3, 3, 3], [2, 3], [8, 8], 2)
NOTE: never use list
as a variable. 注意:永远不要将list
用作变量。 I need that object to do the is list
trick. 我需要该对象来执行is list
技巧。
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