From ce13fd44e8427d64513eee47c2c346deec4979c8 Mon Sep 17 00:00:00 2001
From: pezy <urbancpz@gmail.com>
Date: Wed, 19 Apr 2017 18:26:44 +0800
Subject: [PATCH] init higherOrderFunctions

---
 note_cn/README.md                         |  2 +
 note_cn/higherOrderFunctions.md           | 90 +++++++++++++++++++++++
 note_cn/reference&value.md                |  7 ++
 practice_projects/characterPictureGrid.py | 14 ++++
 practice_projects/commaConnection.py      | 14 ++++
 practice_questions/ch04/README.md         |  0
 6 files changed, 127 insertions(+)
 create mode 100644 note_cn/higherOrderFunctions.md
 create mode 100644 note_cn/reference&value.md
 create mode 100644 practice_projects/characterPictureGrid.py
 create mode 100644 practice_projects/commaConnection.py
 create mode 100644 practice_questions/ch04/README.md

diff --git a/note_cn/README.md b/note_cn/README.md
index 2bd8249..1c6fe9b 100644
--- a/note_cn/README.md
+++ b/note_cn/README.md
@@ -1,2 +1,4 @@
 # 中文笔记
 
+- [引用和值](reference&value.md)
+- [高阶函数专题](higherOrderFunctions.md)
\ No newline at end of file
diff --git a/note_cn/higherOrderFunctions.md b/note_cn/higherOrderFunctions.md
new file mode 100644
index 0000000..61c8258
--- /dev/null
+++ b/note_cn/higherOrderFunctions.md
@@ -0,0 +1,90 @@
+# 高阶函数
+
+在编程语言中, 我们会将一些常用的操作步骤封装起来, 给它个名字. 下次需要用到该操作时, 只需要通过这个名字来调用即可. 这种特性我们称之为函数, 其作为一种基本的抽象手段, 可以将我们从繁琐细碎的低层面操作中解脱出来.
+
+为了让这种抽象手段更加通用, 函数的参数应该也可以是一个函数, 函数的返回值, 也可以是一个函数. 这种参数与返回值涉及到其他函数的函数, 我们就称之为**高阶函数**, 也被称之为**函子**.
+
+高阶函数要比函数更加强悍, 极大程度上增强了编程语言的表现力.
+
+### 函数作为参数
+
+首先, 我们来看一下最简单的一个自然数求和函数:
+
+```python
+def sum_naturals(n):
+    total, k = 0, 1;
+    while k <= n:
+        total, k = total + k, k + 1
+    return total
+```
+
+然后, 需求有点变化, 让你计算立方根的和:
+
+```python
+def sum_cubes(n):
+    total, k = 0, 1
+    while k <= n:
+        total, k = total + k*k*k, k + 1
+    return total
+```
+
+接着, 需求又变了, 让你计算下图所示形式的和:
+
+![](http://composingprograms.com/img/pi_sum.png)
+
+这是一种慢速求解 PI 的方法.
+
+```python
+def pi_sum(n):
+    total, k = 0, 1
+    while k <= n:
+        total, k = total + 8 / ((4*k-3) * (4*k-1)), k + 1
+    return total
+```
+
+此时此刻, 想必你已经复制粘贴三次并修改代码了. 其实我们完全可以抽象出一个更加通用的模版:
+
+```python
+def <name>(n):
+    total, k = 0, 1
+    while k <= n:
+        total, k = total + <term>(k), k + 1
+    return total
+```
+
+抽象出各种 term 的求和过程.
+
+```python
+# template (high-order functions)
+def summation(n, term):
+    total, k = 0, 1
+    while k <= n:
+        total, k = total + term(k), k + 1
+    return total
+
+# functions
+def identity(x):
+    return x
+
+def cube(x):
+    return x*x*x
+
+def pi_term(x):
+    return 8 / ((4*x-3) * (4*x-1))
+
+# refactoring
+def sum_naturals(n):
+    return summation(n, identity)
+
+def sum_cubes(n):
+    return summation(n, cube)
+
+def pi_sum(n):
+    return summation(n, pi_term)
+
+# test
+print(sum_naturals(10)) #55
+print(sum_cubes(3)) #36
+print(pi_sum(1e6)) #3.141592153589902
+```
+
diff --git a/note_cn/reference&value.md b/note_cn/reference&value.md
new file mode 100644
index 0000000..7f33e45
--- /dev/null
+++ b/note_cn/reference&value.md
@@ -0,0 +1,7 @@
+# 引用与值
+
+几乎在任何语言里, 这两者的区分都是组最基础的重点.
+
+Python 里的区别不露痕迹, 对于 `x = y` 这样的式子, x 到底是引用, 还是值, 完全取决于 y 的类型. 如果 y 是字符串, 数值, 元组这种**不可变类型**, x 就是值. 而如果 y 是列表, 字典这样的**可变类型**而言, x 就是引用.
+
+对于列表而言, 如果你想要 copy 值, 就需要显式的调用 `copy()` 方法, 如果要更彻底一些, 连 list 里包含的子 list 也要一起 copy, 那么则需要用到 `deepcopy()` 方法.
\ No newline at end of file
diff --git a/practice_projects/characterPictureGrid.py b/practice_projects/characterPictureGrid.py
new file mode 100644
index 0000000..d8ba3d1
--- /dev/null
+++ b/practice_projects/characterPictureGrid.py
@@ -0,0 +1,14 @@
+grid = [['.', '.', '.', '.', '.', '.'],
+        ['.', 'O', 'O', '.', '.', '.'],
+        ['O', 'O', 'O', 'O', '.', '.'],
+        ['O', 'O', 'O', 'O', 'O', '.'],
+        ['.', 'O', 'O', 'O', 'O', 'O'],
+        ['O', 'O', 'O', 'O', 'O', '.'],
+        ['O', 'O', 'O', 'O', '.', '.'],
+        ['.', 'O', 'O', '.', '.', '.'],
+        ['.', '.', '.', '.', '.', '.']]
+
+for i in range(len(grid[0])):
+    for l in grid:
+        print(l[i], end="")
+    print()
\ No newline at end of file
diff --git a/practice_projects/commaConnection.py b/practice_projects/commaConnection.py
new file mode 100644
index 0000000..40b0fe7
--- /dev/null
+++ b/practice_projects/commaConnection.py
@@ -0,0 +1,14 @@
+spam = ['apple', 'bananas', 'tofu', 'cats']
+
+def list2Str(l):
+    if not l:
+        return ''
+    if len(l) == 1:
+        return l[0]
+    s = ''
+    for i in range(len(l) - 1):
+        s += l[i] + ', '
+    s += 'and ' + l[-1]
+    return s
+
+print(list2Str(spam))
\ No newline at end of file
diff --git a/practice_questions/ch04/README.md b/practice_questions/ch04/README.md
new file mode 100644
index 0000000..e69de29