Python 中产出关键字的用法是什么? 它能做什么?
例如,我试图理解这个代码1:
def _get_child_candidates(self, distance, min_dist, max_dist):
if self._leftchild and distance - max_dist < self._median:
yield self._leftchild
if self._rightchild and distance + max_dist >= self._median:
yield self._rightchild
这就是打电话的人:
result, candidates = [], [self]
while candidates:
node = candidates.pop()
distance = node._get_dist(obj)
if distance <= max_dist and distance >= min_dist:
result.extend(node._values)
candidates.extend(node._get_child_candidates(distance, min_dist, max_dist))
return result
当方法 _get_child_camedates 被调用时会怎样? 列表是否返回? 单一个元素吗? 是否再次调用? 以后的电话何时停止?
1. 本代码由Jochen Schulz(jrschulz)编写,他为公制空间制作了一个伟大的Python图书馆,与完整的源:模块mspace链接。
生成关键字用于查点/字符,其中函数预期将返回一个输出。我想引用这个非常简单的例A:
# example A
def getNumber():
for r in range(1,10):
return r
以上函数只返回一次, 即使它被多次调用。 现在如果我们以收益率替换返回, 如例B :
# example B
def getNumber():
for r in range(1,10):
yield r
当第一次叫2时,它会返回1,当再次叫2时,3,4,然后它会递增到10。
虽然B的例子在概念上是真实的,但要用Python 3来称呼它,我们必须采取以下行动:
g = getNumber() #instance
print(next(g)) #will print 1
print(next(g)) #will print 2
print(next(g)) #will print 3
# so to assign it to a variables
v = getNumber()
v1 = next(v) #v1 will have 1
v2 = next(v) #v2 will have 2
v3 = next(v) #v3 will have 3
收益率与返回率相似。区别是:
函数输出使函数可循环( 在以下示例中, 质数( n= 1) 函数成为可循环的 )。 它基本上意味着下次调用函数时, 它会从它离开的地方( 以产出表达式的线为后方) 继续 。
def isprime(n):
if n == 1:
return False
for x in range(2, n):
if n % x == 0:
return False
else:
return True
def primes(n = 1):
while(True):
if isprime(n): yield n
n += 1
for n in primes():
if n > 100: break
print(n)
在上述例子中, 如果是inprime( n) 是真实的, 它会返回质号。 在下一个迭代中, 它会从下一行继续
n += 1
发电机可以使个别经过处理的物品立即得到处理(不必等待整个收集过程的处理),下面的例子说明了这一点。
import time
def get_gen():
for i in range(10):
yield i
time.sleep(1)
def get_list():
ret = []
for i in range(10):
ret.append(i)
time.sleep(1)
return ret
start_time = time.time()
print('get_gen iteration (individual results come immediately)')
for i in get_gen():
print(f'result arrived after: {time.time() - start_time:.0f} seconds')
print()
start_time = time.time()
print('get_list iteration (results come all at once)')
for i in get_list():
print(f'result arrived after: {time.time() - start_time:.0f} seconds')
get_gen iteration (individual results come immediately)
result arrived after: 0 seconds
result arrived after: 1 seconds
result arrived after: 2 seconds
result arrived after: 3 seconds
result arrived after: 4 seconds
result arrived after: 5 seconds
result arrived after: 6 seconds
result arrived after: 7 seconds
result arrived after: 8 seconds
result arrived after: 9 seconds
get_list iteration (results come all at once)
result arrived after: 10 seconds
result arrived after: 10 seconds
result arrived after: 10 seconds
result arrived after: 10 seconds
result arrived after: 10 seconds
result arrived after: 10 seconds
result arrived after: 10 seconds
result arrived after: 10 seconds
result arrived after: 10 seconds
result arrived after: 10 seconds
