函数无法识别全局变量

Question

我写了一个python脚本，根据弹丸的速度和角度显示弹丸的覆盖距离。

但是，它不会读取另一个函数 (ask_values((( 从用户返回的两个变量。

是什么阻止 covered_distance(( 函数读取用户在 ask_values(( 中输入的 2 个变量(θ 和速度(？

这是程序输出：

Projectile angle:   10
Velocity:       10
Angle: 10.0 Speed: 10.0
Angle: 0.0 Speed: 0.0 
Distance covered: 0.0

这是程序本身：

# IMPORT MODULES
from math import *          # Import all methods/attributes from math module
import sys                  # Import sys.exit()
# DECLARE VARIABLES
theta = 0.0                 # theta = angle at which the projectile is launched
velocity = 0.0              # velocity = speed of the projectile
percent_distance_var = 0.0  # percent_distance_var = percentage of the covered distance
max_distance_var = 0.0      # max_distance_var = maximum distance
covered_distance_var = 0.0  # covered_distance_var = covered distance
# Covered distance
def covered_distance(theta_, velocity_, covered_distance_var_):   # Arguments: (theta, speed, covered_distance_var)
    covered_distance_var_ = 0.2041*((velocity_)**2)*sin(theta_)*cos(theta_) # Calculate 0.2041*((velocity)**2)*sin(theta)*cos(theta)
    data = dict(angle=theta_, speed=velocity_, distance=covered_distance_var_)
    print("Angle: {angle} Speed: {speed} n nDistance covered_: {distance}".format(**data)) # Doesn't print out the correct variables
    return covered_distance_var_         # Return covered_distance_var
# Ask user for values
def ask_values(theta, velocity):
    theta = float(input("Projectile angle: t"))
    velocity = float(input("Velocity: t t"))
    print("Angle: {} Speed: {}".format(theta, velocity)) # Prints out the correct variables
    return(theta, velocity)

def main():# Main method
    ask_values(theta, velocity) # Ask for values
    covered_distance(theta, velocity, covered_distance_var)
# EXECUTE CODE
if __name__ == "__main__":   # If "__main__" statement
    main()  # Main() method

Answer 1

您必须在 main 中捕获函数返回的值，否则它们将被丢弃并且永远不会进入命名空间。当您访问名称时，它在本地找不到任何内容，并查看参数的全局值。所以取而代之的是：

def main():# Main method
    ask_values(theta, velocity) # Ask for values
    covered_distance(theta, velocity, covered_distance_var)

做：

def main():# Main method
    theta, velocity = ask_values(theta, velocity) # Ask for values
    covered_distance(theta, velocity, covered_distance_var)

否则，theta和velocity值将对应于您在此处定义的值：

# DECLARE VARIABLES
theta = 0.0                 # theta = angle at which the projectile is launched
velocity = 0.0              # velocity = speed of the projectile

在全局命名空间中。如果您无论如何都想接受用户输入，那么为这些变量赋值在这里是毫无用处的。Python 不是一种具有变量声明概念的静态类型语言。变量在被赋值时会"出现"。

此外，您可能想要print最终结果：

print(covered_distance(theta, velocity, covered_distance_var))