Python中浮点精度的动态变化

Question

我试图写一个程序，用不同的精度计算pi，并打印出数字和时间。我想打印的结果与当前的准确性，每次。我使用print('pi = %*f'%(i, pi))，i是我当前浮点精度的地方。这使得程序将数字舍入为i十进制数字。我正在附加一张图片，显示运行相同算法的结果，但将输出更改为：

print (" pi = ", pi, " =with ", i-1, " decimal points accuracy= in: ", (-1)*t, "sec")

至：

print (" pi = %.*f"%(i, pi), " =with ", i-1, " decimal points accuracy= in: ", (-1)*t, "sec")

这是我的完整代码：

import time
accuracy = 4
for i in range(1,accuracy + 1):
    pi = 0
    prevPi = 1
    x = 0
    t = time.time()
    while abs((pi * 4) - prevPi) > 10**((-1)*(i+1)):
    #while x < lim:
        prevPi = pi * 4
        pi += (((-1)**(x))/(1+(2*x)))
        #print(abs((pi * 4) - prevPi))
        x += 1
    pi *= 4
    t -= time.time()
    print (" pi = %.*f"%(i, pi), " =with ", i-1, " decimal points accuracy= in: ", (-1)*t, "sec")

​

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如何在没有四舍五入的情况下打印带有i小数的数字？

Answer 1

您可以通过定义截断数字的函数来解决问题。该函数可以采用两个参数：

1. 你想截断的number，
2. 在position，中，它将删除以下所有值。

def truncate(number, position):
    '''Return number with dropped decimal places past specified position.'''
    return number - number%(10**position)

例如，如果希望将数字3.14截断为3.1，则应调用以下命令：

truncate(3.14, -1)

此外，我修改了您的代码，使其更简单，并与PEP 8编码约定匹配。因此，现在它增加了变量命名的清晰度和更好的代码格式。

#!/usr/bin/env python3
'''Module for different pi accuracies calculation time comparison.'''

from time import time

def truncate(number, position):
    '''Return number with dropped decimal places past specified position.'''
    return number - number%(10**position)

def calculate_pi(accuracy):
    '''Return pi with certain floating point accuracy.'''
    previous_pi = 0 
    current_pi = 4 
    iterator = 1 
    while abs(current_pi - previous_pi) > 10 ** (accuracy-1):
        previous_pi = current_pi
        current_pi += 4 * ((-1)**iterator) / (1+(2*iterator))
        iterator += 1
    return truncate(current_pi, accuracy)

def calculation_speed_comparison(max_accuracy):
    '''Print comparison of different accuracy pi calculation time.'''
    for current_accuracy in range(max_accuracy+1):
        calculation_time = time()
        current_pi = calculate_pi(-current_accuracy)
        calculation_time -= time()
        print('pi = {} with {} decimal points accuracy in {} seconds.'.format(
            current_pi, current_accuracy, -calculation_time))

calculation_speed_comparison(4)

对此代码的输出与原始代码非常相似：

pi = 3.0 with 0 decimal points accuracy in 3.266334533691406e-05 seconds.
pi = 3.1 with 1 decimal points accuracy in 0.00016045570373535156 seconds.
pi = 3.14 with 2 decimal points accuracy in 0.0014882087707519531 seconds.
pi = 3.141 with 3 decimal points accuracy in 0.01430201530456543 seconds.
pi = 3.1415 with 4 decimal points accuracy in 0.1466822624206543 seconds.