Python 3.7 中影响数组值的打印语句顺序

Question

如果我在 if 语句集之前打印 pts[0][0]，语句 print("final pts: ", pts) 总是打印一个空数组。但是，如果我在一组 if 语句之后打印 pts[0][0]，则 print("final pts: ", pts) 行会显示正确的值。

我认为它与 pts.pop(0) 行有关，因为它也不能正常工作。当 i = 2 时无法正常工作。

谁能重现这个结果？为什么打印语句会影响列表值？

from matplotlib.lines import Line2D
import matplotlib.pyplot as plt
import numpy as np

x = [10, 24, 23, 23, 3]
y = [12, 2, 3, 4, 2]

skpoints = list(zip(x, y))

for i in skpoints:
    print(i)

limits = np.arange(-1, 2)

pts = []
cutoff = 10
master = []

for i in range(len(skpoints)):
    pts = []
    temp = 1000
    print("\ni: ", i)
    for j in limits:
        try:
            dist = np.sqrt((skpoints[i][0] - skpoints[i + j][0]) ** 2 + (skpoints[i][1] - skpoints[i + j][1]) ** 2)
            print(dist)
            if 0 < dist < temp and (skpoints[i] and skpoints[i+j]) not in pts and dist < cutoff:
                print('pts before if statements', pts[0])

                # if its empty, add point right away
                if not master or not pts:
                    pts.append([dist, skpoints[i], skpoints[i + j]])
                # if dist is smaller than previous distance, replace distance and points
                elif dist < pts[0][0]:
                    pts.pop(0)
                    pts.append([dist, skpoints[i], skpoints[i + j]])
                elif dist == temp and (skpoints[i] and skpoints[i+j]) not in pts:
                    pts.append([skpoints[i], skpoints[i + j]])
                temp = dist
                print('pts after if statements', pts[0])
        except IndexError:
            j -= 1
    print("final pts: ", pts)

Answer 1

问题是你的空白try..catch；你默默地吞下了所有异常，甚至没有打印它们的任何痕迹，这使得调试变得更加困难。

如果 pts 为空，print('pts before if statements', pts[0]) 语句将引发 IndexError 异常，这会绕过循环体的整个其余部分，从而导致完全不同的结果。

Python 3.7 中影响数组值的打印语句顺序

Order of print statements affecting array values in Python 3.7

python

printing

list

try-except