Python变量不变

Question

我正在尝试做一个数据记录代码，让用户输入动物的数量和年龄，出生率和它们在这一代中存活的机会。我曾尝试使用return，但当我运行程序时，变量仍然为0。

在这里，我初始化了变量

Gen0_J=0
Gen0_A=0
Gen0_S=0
Birth_rate=0
Srate_J=0
Srate_A=0
Srate_S=0
New_generations=5

我的第一个函数

def generation_values():
    Gen0_J=int(input("How many juveniles in Generation 0? "))
    Gen0_A=int(input("How many adults in Generation 0? "))
    Gen0_S=int(input("How many seniles in Generation 0? "))
    Srate_J=float(input("What is the survival rate for juveniles? "))
    Srate_A=float(input("What is the survival rate for adults? "))
    Srate_S=float(input("What is the survival rate for seniles? "))
    Birth_rate=int(input("What is the birth rate? "))
    return Gen0_J,Gen0_A,Gen0_S,Srate_J,Srate_A,Srate_S,Birth_rate

显示变量

def display_values():
    print("\nThe amount of juveniles in Generation 0 is",Gen0_J)
    print("The amount of adults in Generation 0 is",Gen0_A)
    print("The amount of seniles in Generation 0 is",Gen0_S)
    print("The birth rate in Generation 0 is",Birth_rate)
    print("The survival rate for juveniles in Generation 0 is",Srate_J)
    print("The survival rate for adults in Generation 0 is",Srate_A)
    print("The survival rate for seniles in Generation 0 is",Srate_S)

generation_values()
display_values()

但是，变量保持为0

How many juveniles in Generation 0? 5
How many adults in Generation 0? 6
How many seniles in Generation 0? 7
What is the survival rate for juveniles? 0.75
What is the survival rate for adults? 1
What is the survival rate for seniles? 0
What is the birth rate? 2

The amount of juveniles in Generation 0 is 0
The amount of adults in Generation 0 is 0
The amount of seniles in Generation 0 is 0
The birth rate in Generation 0 is 0
The survival rate for juveniles in Generation 0 is 0
The survival rate for adults in Generation 0 is 0
The survival rate for seniles in Generation 0 is 0

Answer 1

变量的作用域不正确。[在函数、类或模块中声明的变量在程序的更高级别上是不可访问的-这里是super_biased_man在注释中发布的a short description of python scoping rules ]-在这种情况下，您在generation_values()中赋值的变量是本地定义的。

这样做肯定不是正确的方法，但在generation_values()中声明全局变量将解决您的问题：(定义这样做的“理想方式”取决于您在编程学习中处于什么位置，这会让我们走得太远)

Gen0_J=0
Gen0_A=0
Gen0_S=0
Birth_rate=0
Srate_J=0
Srate_A=0
Srate_S=0
New_generations=5


def generation_values():

    global Gen0_J,Gen0_A,Gen0_S,Srate_J,Srate_A,Srate_S,Birth_rate

    Gen0_J=int(input("How many juveniles in Generation 0? "))
    Gen0_A=int(input("How many adults in Generation 0? "))
    Gen0_S=int(input("How many seniles in Generation 0? "))
    Srate_J=float(input("What is the survival rate for juveniles? "))
    Srate_A=float(input("What is the survival rate for adults? "))
    Srate_S=float(input("What is the survival rate for seniles? "))
    Birth_rate=int(input("What is the birth rate? "))
    return Gen0_J,Gen0_A,Gen0_S,Srate_J,Srate_A,Srate_S,Birth_rate


def display_values():
    print("\nThe amount of juveniles in Generation 0 is",Gen0_J)
    print("The amount of adults in Generation 0 is",Gen0_A)
    print("The amount of seniles in Generation 0 is",Gen0_S)
    print("The birth rate in Generation 0 is",Birth_rate)
    print("The survival rate for juveniles in Generation 0 is",Srate_J)
    print("The survival rate for adults in Generation 0 is",Srate_A)
    print("The survival rate for seniles in Generation 0 is",Srate_S)

generation_values()
display_values()

处理这种情况的另一种方法是将变量作为参数传递给函数，并将赋值的值返回给它们。但是它们很多，传递它们可能会使您的代码变得混乱。

您还可以将它们收集到一个元组中，或者将它们包装在一个类中。

Answer 2

变量的作用域不一致。

你可以这样做：

def generation_values():
    Gen0_J=int(input("How many juveniles in Generation 0? "))
    Gen0_A=int(input("How many adults in Generation 0? "))
    Gen0_S=int(input("How many seniles in Generation 0? "))
    Srate_J=float(input("What is the survival rate for juveniles? "))
    Srate_A=float(input("What is the survival rate for adults? "))
    Srate_S=float(input("What is the survival rate for seniles? "))
    Birth_rate=int(input("What is the birth rate? "))
    return Gen0_J,Gen0_A,Gen0_S,Srate_J,Srate_A,Srate_S,Birth_rate

def display_values(Gen0_J,Gen0_A,Gen0_S,Srate_J,Srate_A,Srate_S,Birth_rate):
    print("\nThe amount of juveniles in Generation 0 is",Gen0_J)
    print("The amount of adults in Generation 0 is",Gen0_A)
    print("The amount of seniles in Generation 0 is",Gen0_S)
    print("The birth rate in Generation 0 is",Birth_rate)
    print("The survival rate for juveniles in Generation 0 is",Srate_J)
    print("The survival rate for adults in Generation 0 is",Srate_A)
    print("The survival rate for seniles in Generation 0 is",Srate_S)

Gen0_J,Gen0_A,Gen0_S,Srate_J,Srate_A,Srate_S,Birth_rate = generation_values()
display_values(Gen0_J,Gen0_A,Gen0_S,Srate_J,Srate_A,Srate_S,Birth_rate)

将是第一步。

这样，"main“名称空间中的变量就与函数中的变量分开了。

消除重复的下一步可能是不关心主命名空间中变量的分隔，只需将它们视为一个元组：

data = generation_values()
display_values(*data)

进一步消除重复和引入清晰度的步骤可以包括：

• 将数据组装到一个对象(命名元组或其他对象)中，并在object

的方法中请求和输出数据

Answer 3

正如其他人所说，问题是对函数内部变量的赋值会创建新的变量，而不是将值赋给全局变量。这就是global关键字存在的原因。

在这种情况下，我会考虑使用一个类，因为您有许多共同操作的相关状态值。

class GenerationData(object):

    def __init__(self, gen_number):
        self.number = gen_number
        self.birth_rate = 0
        self.num_juveniles, self.num_adults, self.num_seniles = 0, 0, 0
        self.juvenile_rate, self.adult_rate, self.senile_rate = 0.0, 0.0, 0.0

    @classmethod
    def read(cls, gen_number):
        gen = cls(gen_number)
        gen.num_juveniles = read_integer(
            'How many juveniles in Generation {}?'.format(gen_number))
        gen.num_adults = read_integer(
            'How many adults in Generation {}?'.format(gen_number))
        gen.num_seniles = read_integer(
            'How many seniles in Generation {}?'.format(gen_number))
        gen.juvenile_rate = read_float(
            'What is the survival rate for juveniles? ')
        gen.adult_rate = read_float('What is the survival rate for adults? ')
        gen.senile_rate = read_float('What is the survival rate for seniles? ')
        gen.birth_rate = read_integer('What is the birth rate? ')

    def display(self):
        print('The amount of juveniles in Generation', self.number,
              'is', self.num_juveniles)
        print('The amount of adults in Generation', self.number,
              'is', self.num_adults)
        print('The amount of seniles in Generation', self.number,
              'is', self.num_seniles)
        print('The birth rate in Generation', self.number,
              'is', self.birth_rate)
        print('The survival rate for juveniles in Generation', self.number,
              'is', self.juvenile_rate)
        print('The survival rate for adults in Generation', self.number,
              'is', self.adult_rate)
        print('The survival rate for seniles in Generation', self.number,
              'is', self.senile_rate)


def read_integer(prompt):
    return int(raw_input(prompt))


def read_float(prompt):
    return float(raw_input(prompt))


first_generation = Generation.read(0)
first_generation.display()

当您操作生成数据时，这将使事情变得更容易，因为它都捆绑到单个对象中。