python for循环

今天在看代码时候遇到了for循环错误，看的百思不得其解，最后又重新翻了翻书才理解。下面看错误分析：

in_channels = [ 768, 192, 192,192,192,]
out_channels = [192,192,192,192,37,]
# zip函数生成[(768,192),(192,192),(192,192),(192,192),(192,37)]
# enumerate函数生成(0，(768,192)), (1,(192,192)) , (2,(192,192)), (3,(192,192)), (4,(192,37))
modules = []
for i, (in_channel, out_channel) in enumerate(
            zip(in_channels, out_channels)):
    modules.append(
        nn.Conv2d(
            in_channels=in_channel,
            out_channels=out_channel,
            kernel_size=1,
            stride=1))
    if i != 4:
        modules.append(nn.Upsample(scale_factor=2, mode='bilinear'))
    print(modules)

in_channels = [ 768, 192, 192,192,192,]
out_channels = [192,192,192,192,37,]
# zip函数生成[(768,192),(192,192),(192,192),(192,192),(192,37)]
# enumerate函数生成(0，(768,192)), (1,(192,192)) , (2,(192,192)), (3,(192,192)), (4,(192,37))
modules = []
for i, (in_channel, out_channel) in enumerate(
            zip(in_channels, out_channels)):
    modules.append(
        nn.Conv2d(
            in_channels=in_channel,
            out_channels=out_channel,
            kernel_size=1,
            stride=1))
    if i != 4:
        modules.append(nn.Upsample(scale_factor=2, mode='bilinear'))
print(modules)

找不同，这两个代码段只有最后一行不同，且缩进不同。造成的结果千差万别：
分别对应第一个和第二个：

[Conv2d(768, 192, kernel_size=(1, 1), stride=(1, 1)), Upsample(scale_factor=2.0, mode=bilinear)]
[Conv2d(768, 192, kernel_size=(1, 1), stride=(1, 1)), Upsample(scale_factor=2.0, mode=bilinear), Conv2d(192, 192, kernel_size=(1, 1), stride=(1, 1)), Upsample(scale_factor=2.0, mode=bilinear)]
[Conv2d(768, 192, kernel_size=(1, 1), stride=(1, 1)), Upsample(scale_factor=2.0, mode=bilinear), Conv2d(192, 192, kernel_size=(1, 1), stride=(1, 1)), Upsample(scale_factor=2.0, mode=bilinear), Conv2d(192, 192, kernel_size=(1, 1), stride=(1, 1)), Upsample(scale_factor=2.0, mode=bilinear)]
[Conv2d(768, 192, kernel_size=(1, 1), stride=(1, 1)), Upsample(scale_factor=2.0, mode=bilinear), Conv2d(192, 192, kernel_size=(1, 1), stride=(1, 1)), Upsample(scale_factor=2.0, mode=bilinear), Conv2d(192, 192, kernel_size=(1, 1), stride=(1, 1)), Upsample(scale_factor=2.0, mode=bilinear), Conv2d(192, 192, kernel_size=(1, 1), stride=(1, 1)), Upsample(scale_factor=2.0, mode=bilinear)]

[Conv2d(768, 192, kernel_size=(1, 1), stride=(1, 1)), Upsample(scale_factor=2.0, mode=bilinear), Conv2d(192, 192, kernel_size=(1, 1), stride=(1, 1)), Upsample(scale_factor=2.0, mode=bilinear), Conv2d(192, 192, kernel_size=(1, 1), stride=(1, 1)), Upsample(scale_factor=2.0, mode=bilinear), Conv2d(192, 192, kernel_size=(1, 1), stride=(1, 1)), Upsample(scale_factor=2.0, mode=bilinear), Conv2d(192, 37, kernel_size=(1, 1), stride=(1, 1))

首先这是for循环缩进错误，正确的是第二个，第一个也没报错，就是不符合逻辑，
print缩进，表示一直循环，直到跳出循环，print不缩进，表示只执行一次
开始modules=[ ],执行第一次循环往里面添加第一个卷积块Conv2d(768, 192），这时正确的应该是继续执行第二次循环，再添加第二个卷积块Conv2d(192, 192），一直添加直到遍历结束。
对于错误的，执行第一次遍历，往module添加第一个卷积块，然后就直接的打印了，同时module里面还放有第一个卷积块，执行第二次遍历，添加第二个卷积块，打印module，此时module里面有两个卷积块，同样，每一次打印都有之前的卷积块，即每次打印都比上一次多一个模块。
所以注意print的缩进，注意打印次数。