如何缩短很多 if 语句？ (Python 3.x)

Question

如何缩短 for 循环中的所有 if 语句？我正在为一个大学项目开发​​这个。我想不出办法。

基本上它应该做的事情是，如果板上的某个位置不等于岩石，则将其设置为植物。这些位置是围绕植物的一个圆圈。示例：

N N N
N P N
N N N

if RainFall == 2:
    print("This summer has been a perfect summer, the plants have multiplied.")
    for Row in range(FIELDLENGTH):
        for Column in range(FIELDWIDTH):
            if Field[Row][Column] == PLANT:
                if Field[Row + 1][Column] != ROCKS:
                    Field[Row + 1][Column] = GOODSUMMER
                if Field[Row - 1][Column] != ROCKS:
                    Field[Row - 1][Column] = GOODSUMMER
                if Field[Row + 1][Column + 1] != ROCKS:
                    Field[Row + 1][Column + 1] = GOODSUMMER
                if Field[Row - 1][Column - 1] != ROCKS:
                    Field[Row - 1][Column - 1] = GOODSUMMER
                if Field[Row][Column + 1] != ROCKS:
                    Field[Row][Column + 1] = GOODSUMMER
                if Field[Row][Column - 1] != ROCKS:
                    Field[Row][Column - 1] = GOODSUMMER
                if Field[Row + 1][Column + 1] != ROCKS:
                    Field[Row + 1][Column - 1] = GOODSUMMER
                if Field[Row - 1][Column + 1] != ROCKS:
                    Field[Row - 1][Column + 1] = GOODSUMMER
                break

Answer 1

是的，将您的索引排列放在一个列表中并对其进行迭代。您可以明确定义列表（对初学者来说更易读，但更容易出错）或使用理解生成它。显式版本优先：

coord_shift = [(1, 0), (-1, 0), (1, 1), (-1, -1), (0, 1), (0, -1), (1, -1), (-1, 1)]
for Row in range(FIELDLENGTH):
    for Column in range(FIELDWIDTH):
        if Field[Row][Column] == PLANT:
            for i, j in coord_shift:
                if Field[Row + i][Column + j] != ROCKS:
                    Field[Row + i][Column + j] = GOODSUMMER

一些补充说明：

推荐的 Python 风格是对常规变量使用小写的变量名，大写的人更适合类。

你不需要休息。

上面提到了Field[Row +1][Column -1] 的小错误。

我承诺的冒险版本是：

coord_shift = [(i, j) for i in range(-1, 2) for j in range (-1, 2)]
coord_shift.drop((0, 0))

Answer 2

我们只能猜测您的其余代码，因此下面包含了用于测试目的的完整实现。要查看您重新编写的代码，请查看 multiply_plants 函数。它没有使用许多if 语句，而是使用循环来检查单元格周围的区域。您可能还会注意到，它正确检查了每个列表的边界，因此不会发生 IndexError 异常。

#! /usr/bin/env python3
import random


FIELD_ROWS = 10
FIELD_COLUMNS = 10
EMPTY = ' '
PLANT = 'P'
ROCKS = 'R'
NEW_PLANT = 'N'


def main():
    field = create_field()
    show_field(field)
    multiply_plants(field, 2)
    replace_cells(field, NEW_PLANT, PLANT)
    show_field(field)


def create_field():
    field = []
    for _ in range(FIELD_ROWS):
        row = []
        for _ in range(FIELD_COLUMNS):
            row.append(random.choice([EMPTY] * 3 + [ROCKS] * 2 + [PLANT] * 1))
        field.append(row)
    return field


def show_field(field):
    width = max(map(len, field)) * 2 + 1
    print(f'/{"-" * width}\\')
    print('\n'.join(' '.join(['|'] + row + ['|']) for row in field))
    print(f'\\{"-" * width}/')


def multiply_plants(field, rainfall):
    # If there was enough rain, cause the plants to spread.
    if rainfall > 1:
        print('This summer has been a perfect summer;')
        print('the plants have multiplied!')
        # Find each space that already has a plant in it.
        for y, row in enumerate(field):
            for x, cell in enumerate(row):
                if cell == PLANT:
                    # Introduce a Y-axis offset to search up & down.
                    for y_offset in range(-1, 2):
                        y_index = y_offset + y
                        if 0 <= y_index < len(field):
                            # Introduce a X-axis offset to search left & right.
                            for x_offset in range(-1, 2):
                                if y_offset or x_offset:    # Skip zero offset.
                                    x_index = x_offset + x
                                    if 0 <= x_index < len(field[y_index]):
                                        # Spread plant to non-rock areas.
                                        if field[y_index][x_index] != ROCKS:
                                            field[y_index][x_index] = NEW_PLANT


def replace_cells(field, old, new):
    for y, row in enumerate(field):
        for x, cell in enumerate(row):
            if cell == old:
                field[y][x] = new


if __name__ == '__main__':
    main()