如何使用python进行二分查找算法？

def binarySearch(alist, item):
 first = 0
 last =
len(alist)-1
 found = False
 while first<=last
and not found:
midpoint = (first + last)//2
if alist[midpoint] == item:
  found = True
else:
  if item < alist[midpoint]:
 last = midpoint-1
  else:
 first = midpoint+1
 return found
testlist = [0, 1, 2, 8, 13, 17, 19, 32, 42,]
print(binarySearch(testlist, 3))
print(binarySearch(testlist, 13))

def binSearch(lst, item):
 mid = len(lst) //2
 found = False
 if lst[mid] ==
item:
 found = True
 return found
 if mid == 0:
#mid等于0就是找到最后一个元素了。
 found = False
 return found
 else:
 if item > lst[mid]: #找后半部分
  #print(lst[mid:])
  return
binSearch(lst[mid:], item)
 else:
  return
binSearch(lst[:mid], item) #找前半部分