Basic/切片用法.ipynb

切片用法.ipynb

{
  "cells": [
    {
      "metadata": {},
      "cell_type": "markdown",
      "source": "### 切片用法\n\n模式[start:end:step]    "
    },
    {
      "metadata": {},
      "cell_type": "markdown",
      "source": "#### 读取"
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l = [1,2,3,4,5,6,7,8]",
      "execution_count": 106,
      "outputs": []
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[:] # 取全部元素",
      "execution_count": 107,
      "outputs": [
        {
          "data": {
            "text/plain": "[1, 2, 3, 4, 5, 6, 7, 8]"
          },
          "execution_count": 107,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[::-1] # 逆序",
      "execution_count": 108,
      "outputs": [
        {
          "data": {
            "text/plain": "[8, 7, 6, 5, 4, 3, 2, 1]"
          },
          "execution_count": 108,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[::2] # 取下标为偶数位的元素",
      "execution_count": 109,
      "outputs": [
        {
          "data": {
            "text/plain": "[1, 3, 5, 7]"
          },
          "execution_count": 109,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[1::2] # 下标为奇数位",
      "execution_count": 110,
      "outputs": [
        {
          "data": {
            "text/plain": "[2, 4, 6, 8]"
          },
          "execution_count": 110,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[2:4] # 下标为 [2,4)",
      "execution_count": 111,
      "outputs": [
        {
          "data": {
            "text/plain": "[3, 4]"
          },
          "execution_count": 111,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[:3] # 取前3位，下标为 [0,3) ",
      "execution_count": 112,
      "outputs": [
        {
          "data": {
            "text/plain": "[1, 2, 3]"
          },
          "execution_count": 112,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[:100] # 超过数组长度时，尾部截断",
      "execution_count": 113,
      "outputs": [
        {
          "data": {
            "text/plain": "[1, 2, 3, 4, 5, 6, 7, 8]"
          },
          "execution_count": 113,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[100:0] # 起始位置大于长度时，返回空list ",
      "execution_count": 132,
      "outputs": [
        {
          "data": {
            "text/plain": "[]"
          },
          "execution_count": 132,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[-3:] # 取后3位，下标为 [n-3,n)",
      "execution_count": 114,
      "outputs": [
        {
          "data": {
            "text/plain": "[6, 7, 8]"
          },
          "execution_count": 114,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[3:] # 下标为 [3，n)",
      "execution_count": 115,
      "outputs": [
        {
          "data": {
            "text/plain": "[4, 5, 6, 7, 8]"
          },
          "execution_count": 115,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[:-3] # 下标为 [0, n-3) ",
      "execution_count": 116,
      "outputs": [
        {
          "data": {
            "text/plain": "[1, 2, 3, 4, 5]"
          },
          "execution_count": 116,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[3] # 取下标为3",
      "execution_count": 117,
      "outputs": [
        {
          "data": {
            "text/plain": "4"
          },
          "execution_count": 117,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[-3] #l[n-3]=l[5] #取下标为n-3的数",
      "execution_count": 118,
      "outputs": [
        {
          "data": {
            "text/plain": "6"
          },
          "execution_count": 118,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[-1] # 最后一个数，即下标为n-1的数",
      "execution_count": 119,
      "outputs": [
        {
          "data": {
            "text/plain": "8"
          },
          "execution_count": 119,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[2::3] # 每隔3取一个数",
      "execution_count": 120,
      "outputs": [
        {
          "data": {
            "text/plain": "[3, 6]"
          },
          "execution_count": 120,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "for i in range(3):\n    print(l[i:i+3]) # 窗口式读取，每次读3个数，循环3次 ",
      "execution_count": 121,
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": "[1, 2, 3]\n[2, 3, 4]\n[3, 4, 5]\n"
        }
      ]
    },
    {
      "metadata": {},
      "cell_type": "markdown",
      "source": "#### 修改"
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[0] = 'a' #替换l[0]\nl ",
      "execution_count": 122,
      "outputs": [
        {
          "data": {
            "text/plain": "['a', 2, 3, 4, 5, 6, 7, 8]"
          },
          "execution_count": 122,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {},
      "cell_type": "markdown",
      "source": "#### 插入"
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[3:3] = 'c' # 在l[3]处插入元素\nl ",
      "execution_count": 123,
      "outputs": [
        {
          "data": {
            "text/plain": "['a', 2, 3, 'c', 4, 5, 6, 7, 8]"
          },
          "execution_count": 123,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[:0]= 'a' # 头部插入\nl ",
      "execution_count": 124,
      "outputs": [
        {
          "data": {
            "text/plain": "['a', 'a', 2, 3, 'c', 4, 5, 6, 7, 8]"
          },
          "execution_count": 124,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[len(l):0]= 'x' # 尾部插入\nl ",
      "execution_count": 125,
      "outputs": [
        {
          "data": {
            "text/plain": "['a', 'a', 2, 3, 'c', 4, 5, 6, 7, 8, 'x']"
          },
          "execution_count": 125,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {},
      "cell_type": "markdown",
      "source": "#### 替换"
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[:4] = ['e','f'] # 替换，前4位替换为2位\nl ",
      "execution_count": 126,
      "outputs": [
        {
          "data": {
            "text/plain": "['e', 'f', 'c', 4, 5, 6, 7, 8, 'x']"
          },
          "execution_count": 126,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[-3:] = ['x','y','z'] # 最后3位替换为其他3位\nl ",
      "execution_count": 127,
      "outputs": [
        {
          "data": {
            "text/plain": "['e', 'f', 'c', 4, 5, 6, 'x', 'y', 'z']"
          },
          "execution_count": 127,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[::2] = [0]*5 # 奇数为置0，间隔替换时，长度需要相等 \nl ",
      "execution_count": 128,
      "outputs": [
        {
          "data": {
            "text/plain": "[0, 'f', 0, 4, 0, 6, 0, 'y', 0]"
          },
          "execution_count": 128,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {},
      "cell_type": "markdown",
      "source": "#### 删除"
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "l[:2] = [] #删除前2位元素\nl ",
      "execution_count": 129,
      "outputs": [
        {
          "data": {
            "text/plain": "[0, 4, 0, 6, 0, 'y', 0]"
          },
          "execution_count": 129,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "del l[:2] # 删除前2位元素\nl ",
      "execution_count": 130,
      "outputs": [
        {
          "data": {
            "text/plain": "[0, 6, 0, 'y', 0]"
          },
          "execution_count": 130,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    },
    {
      "metadata": {
        "trusted": false
      },
      "cell_type": "code",
      "source": "del l[::2] # 删除奇数位元素\nl ",
      "execution_count": 131,
      "outputs": [
        {
          "data": {
            "text/plain": "[6, 'y']"
          },
          "execution_count": 131,
          "metadata": {},
          "output_type": "execute_result"
        }
      ]
    }
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