[Python03]-基础知识点
Python官网有一个基础入门教程，后面还有一个类似考试的题目。这个教程语言很生动，学习起来也比较轻松，感觉很好，这里把学习到的一些基础知识点做一个总结，希望作为一个备忘，感兴趣的同学可以转载。
1.输出
>>> print("This is the first python program.")
This is the first python program.
>>> print "Hello Python"
Hello Python
>>>
注：这两种方式都支持，但3.0以上版本的python只支持第一种方式。
2.注释
>>> print("not commnet")
not commnet
>>> #print("comment")
>>>
'''
print("We are in a comment")
print ("We are still in a comment")
'''
print("We are out of the comment")注：单行注释是#（与powershell一致），多行注释是三个单引号
3.变量
>>> a = 1 >>> print(a) 1 >>> str = "hello" >>> print str hello >>> c = 2 >>> print(a+c) 3 >>> print(type(a)) <type 'int'> >>> print(type(str)) <type 'str'> >>> d = "3" >>> print(a+int(d)) 4 >>>注：python变量的类型是弱类型的，即声明变量时不需要指定类型，这个跟powershell类似。type函数是获取变量类型的，在变量前面加int,str是进行类型强制转换。
4.运算符
>>> print (3 + 4) 7 >>> print (3 - 4) -1 >>> print (3 / 4) 0 >>> print (3 * 4) 12 >>> print (3 ** 4) 81 >>> print(81//4) 20 >>> a = 0 >>> a += 2 >>> print(a) 2注：3**4 是3的4次方，//表示求最大商,+=操作和其他语言相同
5.if...else
a = 20
if a >= 22:
print("if")
elif a >= 21:
print("elif")
else:
print("else")注：if后面的:不要忘记，主要elif的写法有点特殊
6.函数定义及使用
def someFunction():
print("foo")
someFunction()
</span><span style="font-family:Microsoft YaHei;">
def someFunction2(a, b):
print(a+b)
someFunction2(12,451)
注：不要忘记:，传参数方式跟其他函数相同。
7.循环
for a in range(1,3):
print (a)
a = 1
while a < 10:
print (a)
a+=1注：第一种是for循环，跟常见的形式不太一样，第二种是while循环，比较常见的形式。
8.字符串操作
>>> strVar = "hello"
>>> print(strVar.count('l'))
2
>>> print(strVar.find('h'))
0
>>> print(strVar.upper())
HELLO
>>> print(strVar.lower())
hello
>>> print(strVar.replace('l','m'))
hemmo
>>> print(strVar.strip())
hello
>>>注：strip()是去除首尾空格
9.列表
>>> sampleList = [1,2,3,4,5,6,7,8]
>>> print(sampleList)
[1, 2, 3, 4, 5, 6, 7, 8]
>>> sampleTuple = ("a","b","c")
>>> print(sampleTuple)
('a', 'b', 'c')
>>> sampleList.append(9)
>>> print(sampleList)
[1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> sampleTuple.append("d")
Traceback (most recent call last):
File "<pyshell#44>", line 1, in <module>
sampleTuple.append("d")
AttributeError: 'tuple' object has no attribute 'append'
>>>注：
Python的列表有两种，list 是允许append的，但是tupe是不允许append的。但是如果确实需要append tuple，先将tuple转换成list再调用append即可；
10.字典
>>> myDic = {'username':"Austin",'age':20}
>>> print(myDic["username"])
Austin
>>> print(myDic["age"])
20
>>> for d in myDic:
print(d,myDic[d])
('username', 'Austin')
('age', 20)
>>>注：字典属于key/value类型的数据结构，用法比较常见。
11.异常处理
var1 = '1'
try:
var1 = var1 + 1 # since var1 is a string, it cannot be added to the number 1
except:
print(var1, " is not a number") #so we execute this
print(var1)
var1 = '1'
try:
var2 = var1 + 1 # since var1 is a string, it cannot be added to the number 1
except:
var2 = int(var1) + 1
print(var2)注：这里不是catch，而是except，注意书写形式
12.读文件
f = open("test.txt","r") #opens file with name of "test.txt"
print(f.readline())
print(f.readline())
f.close()
I am a test file.
Maybe someday, he will promote me to a real file.</span>
f = open("test.txt","r") #opens file with name of "test.txt"
myList = []
for line in f:
myList.append(line)
print(myList)
f.close()
['I am a test file.\n', 'Maybe someday, he will promote me to a real file.\n', 'Man, I long to be a real file\n', 'and hang out with all my new real file friends.']
注：r 是读的意思，w是写的意思。不要忘记关闭管道！！
13.写文件
f = open("test.txt","w") #opens file with name of "test.txt"
f.close()
#the file content will be cleared!!!
f = open("test.txt","w") #opens file with name of "test.txt"
f.write("I am a test file.")
f.write("Maybe someday, he will promote me to a real file.")
f.write("Man, I long to be a real file")
f.write("and hang out with all my new real file friends.")
f.close()
f = open("test.txt","a") #opens file with name of "test.txt"
f.write("and can I get some pickles on that")
f.close()注意：
使用w时，open的时候会将文件已有的内容清空！！！
14.类
#ClassOne.py
class Calculator(object):
#define class to simulate a simple calculator
def __init__ (self):
#start with zero
self.current = 0
def add(self, amount):
#add number to current
self.current += amount
def getCurrent(self):
return self.current
calc = Calculator()
print(calc.add(2))
print(calc.getCurrent())
注：类的定义形式跟常见的形式比较不同