#! /usr/bin/env python3
# coding: utf-8
import numpy as np
def im2col(input_data, filter_h, filter_w, stride=1, pad=0):
    N, C, H, W = input_data.shape
    out_h = (H + 2*pad - filter_h)//stride + 1
    out_w = (W + 2*pad - filter_w)//stride + 1
    img = np.pad(input_data, [(0,0), (0,0), (pad, pad),
                 (pad, pad)], 'constant')
    col = np.zeros((N, C, filter_h, filter_w, out_h, out_w))
    for y in range(filter_h):
        y_max = y + stride*out_h
        for x in range(filter_w):
            x_max = x + stride*out_w
            col[:, :, y, x, :, :] = \
               img[:, :, y:y_max:stride, x:x_max:stride]
    col = col.transpose(0, 4, 5, 1, 2, 3).reshape(N*out_h*out_w, -1)
    return col

x1 = np.random.rand(1,3,7,7)
col1 = im2col(x1,5,5,stride=1,pad=0)
print(col1.shape)

x2 = np.random.rand(10,3,7,7)
col2 = im2col(x2,5,5,stride=1,pad=0)
print(col2.shape)