python - Beginning Python fibonacci generator

Question

I'm trying to make a fibonacci number generator that stops at a given amount, but it usually goes past the amount. What am I doing wrong?

#Fibonacci number generator
a=0
b=1
print("Fibonacci number generator.")
stopNumber=input("How high do you want to go? If you want to go forever, put n.")
print(1)
while stopNumber=="n":
        a=a+b
        b=b+a
        print(a)
        print(b)
else:
    while int(stopNumber) > a or int(stopNumber) > b:
        a=a+b
        b=b+a
        print(a)
        print(b)

Answer 1

您获得更高值的原因是因为您拥有a = a+b和b = b+a在一个循环中。因此，当您检查while int(stopNumber) > a or int(stopNumber) > b:获取True并进入循环中的值时，a = a+b并且b = b+a可以使 和 的值a大于b并且stopNumber由于您在不检查的情况下打印它，因此您将获得一些更高的值。您应该在循环中只增加一次，如果您在 while 循环之后编写 print 语句，您将不会得到正确的值

prev = 0                             
curr = 1
print("Fibonacci number generator.")
stopNumber = input("How high do you want to go? If you want to go forever, put n.")
if stopNumber == 'n':                    
    print(curr)                     
    curr = prev + curr
    prev = curr
else:
    while curr<stopNumber:
        print(curr)
        curr = prev + curr
        prev = curr

注意：如果输入为 ，代码将永远运行n。

Answer 2

同样，工作并使用更智能的技术：

# returns generator
def fib(stop):
    prev, current = 0, 1
    while current < stop:  # a little hack here - python is ok comparing ints to floats
        yield current
        # multiple assginment - operands on the left are "frozen" just before theis instruction
        prev, current = current, prev + current 

# note inf - float('inf') results in "positive infinity" which is an appropriate math concept for "forever"
stop = float(input("How high do you want to go? If you want to go forever, put inf."))

for f in fib(stop):
    print (f)

注意：请不要尝试这样做list(fib(float('inf'))):)

Answer 3

您检查 stopNumber > a 或 b，然后增加 a 和 b，打印它们。如果您只想在它们是 <= stopNumber 时打印它们，而不是执行以下操作：

#Fibonacci number generator
a=0
b=1
print("Fibonacci number generator.")
stopNumber=input("How high do you want to go? If you want to go forever, put n.")
print(1)
while stopNumber=="n":
        a=a+b
        b=b+a
        print(a)
        print(b)
else:
    while True:
        a = a+b
        b = b+a
        if int(stopNumber) >= a:
           print(a)
        if int(stopNumber) >= b:
           print(b)
        else:
          break

Answer 4

使用您的代码：

#Fibonacci number generator
a=0
b=1
print("Fibonacci number generator.")
stopNumber=input("How high do you want to go? If you want to go forever, put n.")
print(1)
while stopNumber=="n" or int(stopNumber) > a+b:
    a, b = b, a+b
    print(b)

Answer 5

 #This is a simple yet efficient program using recursion:

def fibonacci_rec(a, b):
    if a >= 0 and b > 0 or a > 0 and b >= 0:
        s = [a, b]
        while a+b <= 1000: #can set any upper boundary  
            f = a+b
            a = b
            b = f
            s.append(f)
            fibonacci_rec(a, b)
        return s
    else:
        return 'Invalid'

print(fibonacci_rec(1, 1))  # You can set any value of a and b, as you like and no need to iterate in here, just call function once and it does the iteration for you! 

Answer 6

第二个“while”循环始终保持运行，“a”或“b”低于“stopNumber”。因此，循环继续运行，直到“a”和“b”都大于“stopNumber”。结果，当“b”大于“stopLimit”但“a”仍低于“stopLimit”时，循环继续运行。因此，要应用的第一个解决方法是将“或”条件更改为“和”条件。

您只是在总和之前检查条件是否适用。然后，当总和完成时，它们的结果可能大于“stopLimit”；这就是您打印的内容。要解决此问题，您可以添加“if”语句来验证总和结果是否仍低于“stopNumber”。

以下是这些修复后代码的外观：

#Fibonacci number generator
a=0
b=1
print("Fibonacci number generator.")
stopNumber=input("How high do you want to go? If you want to go forever, put n.")
print(1)
while stopNumber=="n":
        a=a+b
        b=b+a
        print(a)
        print(b)
else:
    while int(stopNumber) > a and int(stopNumber) > b:
        a=a+b
        b=b+a
        if int(stopNumber) > a:
            print(a)
        if int(stopNumber) > b:
            print(b)

Answer 7

def fib(n):
    if n == 0:
        return 0
    if n == 1:
        return 1
    return fib(n-1) + fib(n-2)

print("Fibonacci number generator.")
stopNumber=input("How high do you want to go? If you want to go forever, put n.")
if stopNumber == 'n':
    i=1
    while True:
        print 'Fibonacci #{0}: {1}'.format(i, fib(i))
        i=i+1
else:
    for i in range(1,int(n)):
        print 'Fibonacci #{0}: {1}'.format(i, fib(i))