[英]Implementing recursive function with __iter__ method in a Python class
所以我正在解決一個問題,我要創建一個 Python Class 來生成列表的所有排列,我遇到了以下問題:
謝謝!
class permutations():
def __init__(self, ls):
self.list = ls
def __iter__(self):
ls = self.list
length = len(ls)
if length <= 1:
yield ls
else:
for p in self.list_all(ls[1:]):
for x in range(length):
yield p[:x] + ls[0:1] + p[x:]
def list_all(self, ls):
length = len(ls)
if length <= 1:
yield ls
else:
for p in self.list_all(ls[1:]):
for x in range(length):
yield p[:x] + ls[0:1] + p[x:]
只需從__iter__
調用self.list_all
:
class permutations():
def __init__(self, ls):
self.list = ls
def __iter__(self):
for item in self.list_all(self.list):
yield item
def list_all(self, ls):
length = len(ls)
if length <= 1:
yield ls
else:
for p in self.list_all(ls[1:]):
for x in range(length):
yield p[:x] + ls[0:1] + p[x:]
您的list_all
方法已經是一個生成器,因此您可以直接在__iter__
中返回它:
class permutations():
def __init__(self, ls):
self.list = ls
def __iter__(self):
return self.list_all(self.list)
def list_all(self, ls):
length = len(ls)
if length <= 1:
yield ls
else:
for p in self.list_all(ls[1:]):
for x in range(length):
yield p[:x] + ls[0:1] + p[x:]
這既閱讀起來更清晰,執行速度也更快。
您還可以選擇在__iter__
中定義list_all
。
class permutations2():
def __init__(self, ls):
self.list = ls
def __iter__(self):
def list_all(ls):
length = len(ls)
if length <= 1:
yield ls
else:
for p in list_all(ls[1:]):
for x in range(length):
yield p[:x] + ls[0:1] + p[x:]
return list_all(self.list)
時序permutations
與我的permutations2
給出了幾乎相同的結果。
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