Learning

Errors

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+#1、a=[1,2,3,4,5]。则     a[5:0]==[] , 而不会报错

README.md

@@ -1,2 +1,4 @@
 # Learning
-Some exersices of learing and notes.
+# Some exersices of learing and notes.
+
+# Don't now what should I say.Just do something change to test the function.

differences

@@ -1,4 +1,13 @@
 # Here are some differences between Python2.7 and Python 3,which may lead to bug.
+
 #1、In Python 2.7,You can use "print \'str'".But in Python 3,after "print" you must use() to complete this statement.
+
 #2、In Python 2.7,generator.next().In Python 3,next(generator).
-#3、In python 2.7,what function "filter" returns is a list.But in python 3,what function "filter"returns is a generator.
+
+#3、In python 2.7,what function "filter" returns is a list.But in python 3,what function "filter"returns is a generator.(test2.py)
+
+#4、In python 2.7,None.split() will cause error.But in python 3,None.split() == ''(test2.py)
+
+#5、In python 3,There is a function "nonlocal".But in python 2.7,it doesn't exist.(test4.py)
+
+#6、In python 3,type(3)returns <class'int'>.In python 2.7,it returns <type'int'>.(Which may explain sth between class and type?)

test1.py

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+#! /usr/bin/env python
+# -*- coding=utf-8 -*-
+
+"""
+练习map和reduce函数
+"""
+from functools import reduce
+
+def str2float(s):
+    a1,a2 = s.split('.') #分隔符split()
+    def string(s):
+        dight = {'0':0,'1':1,'2':2,'3':3,'4':4,'5':5,'6':6,'7':7,'8':8,'9':9}#字典用{}
+        return dight[s]
+    def num1(x,y):
+        return x*10+y
+    def num2(x,y):
+        return x/10.0+y  #此处高能注意！x为整数，若x/10，则结果为0，所以此处采用/10.0，计算结果为小数
+    zheng = reduce(num1,map(string,a1))
+    xiao = reduce(num2,map(string,reversed(a2))) #字符串反转reversed(),注意reversed反转结果为iterator,要用list显示出
+    return num2(xiao,zheng)
+
+print('str2float(\'123,456\') =',str2float('123.456'))
+if abs (str2float('123.456') - 123.456) < 0.000001:
+    print "测试成功!"
+else:
+    print "测试失败"
+

test2.py

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+#/usr/bin/env python
+# -*- coding:utf-8 -*-
+
+"""
+  测试filter函数
+"""
+#  在3.0中 filter结果为iterator；2.7中则为list。所以如求素数的代码，循环过后就出问题，因为list没有next
+"""
+def not_empty(s):
+    return s and s.split()    #""=false,所以此处判定结果ok
+
+print list(filter(not_empty,['A','','B','C',' '])) #此处出了点小问题，原题有None,None.split()会报错，python3.0则不会
+#引申，filter(None,a)会保留a中所有为真的元素,''、0等则会被剔除
+"""
+
+"""
+
+def _odd_iter():
+    n = 1
+    while True:
+        n = n + 2
+        yield n
+
+def _not_divisible(n):
+    return lambda x:x % n >0
+
+def primes():
+    yield 2
+    it = _odd_iter()
+    while True:
+        n = it.next()
+        yield n
+        it = filter(_not_divisible(n),it)
+
+
+for n in primes():
+    if n < 1000:
+        print(n)
+    else:
+      break
+"""
+def is_palindrome(n):
+    string=str(n)
+    length = len(string)
+    if length == 1:
+        return True
+    else:
+        for i in range(0,length//2+1):
+            if string[i] != string[length-i-1]: #小心，string索引最大为length-1，不是length
+                return False
+        return True
+
+output = filter(is_palindrome,range(1,1000))
+print('1~1000:', list(output))
+if list(filter(is_palindrome, range(1, 200))) == [1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 22, 33, 44, 55, 66, 77, 88, 99, 101, 111, 121, 131, 141, 151, 161, 171, 181, 191]:
+    print('测试成功!')
+else:
+    print('测试失败')

test4.py

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+#! /usr/bin/env python
+# -*- coding=utf-8 -*-
+
+"""
+  测试sorted函数
+
+L=[('Bob',75),('Adam',92),('Bart',66),('Lisa',88)]
+def by_name(t):
+    return t[0].lower()
+
+def by_score(t):
+    return -t[1]
+
+print sorted(L,key=by_name)
+print sorted(L,key=by_score)
+"""
+'''
+  闭包
+'''
+def CreateCounter():
+    i = [0]
+    def counter():
+        i[0] =i[0] + 1  #这一行不能放到return i[0]后面，用i[0]是因为int(i)无法调用,（外部变量），在python3.0中有函数nonlocal解决调用外部变量的问题
+        return i[0]
+    return counter
+
+counterA = CreateCounter()
+print(counterA(),counterA(),counterA(),counterA())
+counterB=CreateCounter()
+if [counterB(),counterB(),counterB(),counterB()] == [1,2,3,4]:
+    print '测试通过!'
+else:
+    print "测试失败"