Python Base One
//this is my first day to study python, in order to review, every day i will make notes (2016/7/31)
1. In python , there are many bulit-in funcation. you can use follow to find out hou many built-in funcation:
dir(__builtins__)
if you want get BIF detail, you can use follow code:
help(……) such as help(input),int()
2. In python, you should be care to indent, if not , it will appear a lots error.
such as follow ,because indent error ,it will appear an error:
temp = input('input a num you want:')
guess = int(temp)
if guess == 8:
print('you are right')
else:
print('you are wrong')
3. In python , when you define variable ,uppercase and lowercase is different.
such as:
temp = 'roy'
Temp = 'wyg'
temp and Temp is not same variable
4. In python , if you want to use ' in a string ,you can user escape charcters : \
such as:
print('Let\'s go!')
5. In python , origin string is userful , maybe the follow result is not you except
such as :
str = 'c:\now\data'
print(str)
result is :
c:
ow\data
you can solve this problem by str = r'c:\now\data' ,this code is equal to str = 'c:\\now\\data'
when you print(str), the result will be c:\now\data
6. In python , if a string , you want to change row ,you can user ''' ,if you not user ''' and change row ,it will appear an error
such as:
str = '''this
is
me'''
print(str)
the result is :
this
is
me
7. In python , import module , such as if you want a rand num , range is 1-10 and type is int ,how to achieve it
import random
randnum = random.randint(1,10)
//this is second day to study python(2016/8/1)
8. In python , we can see 'e' as 10
such as:
1.5e4 == 15000.0
9. In python , type conversion is userful , the follow is base conversion
float or string -> int
such as :
a = '26' b = int(a) print(b) -> 26
a = 'qq' b = int(a) error
a = 3.14 b = int(a) print(b) -> 3
----------------------------------------
int or string -> float
such as:
a = '26' b = float(b) print(b) -> 26.0
a = 'qq' b = float(b) error
a = 26 b = float(b) print(b) -> 26.0
------------------------------------------
int or float -> str
such as:
a = 26 b = str(a) print(b) -> '26'
a = 3.14 b = str(a) print(b) -> '3.14'
a = 5e19 b = str(a) print(b) -> '5e+19'
sometimes, we need to be care to str,
such as:
str = 'I like apple'
print(str) -> 'I like apple'
but if it is c = str(5e19) ,it will appear an error ,because str is BIF ,we define str again , it will have new means, so it will have error
10. In python ,we can get the type of variable
such as:
a = 'qq'
type(a) -> <class 'str' at 0x----->
a = 3.0
type(a) -> <class 'float' at 0x--->
a = True
type(a) -> <class 'bool' at 0x--->
we recommand follow:
a = 'roy'
isinstance(a, str) -> True
isinstance(a, int) -> False
but sometimes you need to know it maybe account an error:
TypeError: isinstance() arg 2 must be a type or tuple of types
the reason is may you define str before, In python ,you can change built-in funcation, so when you define variable ,you should try to avoid user special chararctes. such as try not to use BIF.
11. In python , arithmetic operators has + - * / ** // %
a += 4 <==> a = a + 4
a = 2
b = 3
a / b -> 0.6666666666666666
a // b -> 0
b // a -> 1
a % b -> 2
b % a -> 1
a * b -> 8
b ** a -> 9
12. In python , logical operators includes and , or , not
such as:
not Ture
False
13. In python , if and else how to use:
score = int(input('please input score:'))
if 90<= score <= 100:
print('A')
elif 80<= score < 90:
print('B')
elif 60<= score < 80:
print('C')
else:
print('D')
14. trinocular operator
small = x if x < y else y
->
x, y = 4, 5
if x < y:
small = x
else:
small = y
15. assert ,when condication is false , it will have assertionerror
such as:
assert 3 > 4
>>> assert 3>4
Traceback (most recent call last):
File "<pyshell#1>", line 1, in <module>
assert 3>4
AssertionError
//third day study python (2016/8/2)
16. In python , how to achieve 'for' loop:
for target in expression:
loop body
such as:
string = 'roy'
for i in string:
print(i)
->
r
o
y
students = ['wyg' , 'roy]
for each in students:
print(each,len(each))
17. In python , range() is often combined with for loop , what's range()
range([start,] stop [, step = 1]) // three para
[] represent select
step = 1 represent by default step is 1
so it is from start to stop number list
range(3) -> range(0,3)
list(range(4)) -> [0, 1, 2, 3]
for i in range(2,5):
print(i)
result is :2 3 4
for i in range(1,10,4):
print(i)
result is :1 5 9
18. In python , there are also have break and continue
continue skip current loop
break end loop
19. In python , there are no array ,but have list and more power
such as:
mixType = [1, 'roy', 3.14, [5, 6]]
we can also create an empty list:
empty = []
how to add content to list:
empty.appen(3) -> 3
or
empty.extend([3, 6, 9]) -> 3 3 6 9
or
empty.insert(0, 'aaa') -> 3 'aaa 3 6 9
how to get value according to subscript：
empty[0] -> 3
how to delete value
empty.remove(9) -> 3 'aaa' 3 6
or
del temp[1] -> 3 3 6
if you want to delete from memary , you can use del temp
or
temp.pop() -> [3, 3]
you also can pop value according to subscript
such as :temp.pop(1)
slice is useful ,you can achieve amazing thing:
such as :
aaa = [1, 2, 3, 4, 5, 6]
aaa[1:4] -> [2,3,4]
aaa[:3] -> [1,2,3]
aaa[1:] -> [2,3,4,5,6]
aaa[:] = [1,2,3,4,5,6]
aaa -> [1,2,3,4,5,6]
20. In python , how to compare to list
list1 = [123,456]
list2 = [234,345]
list1 > list2
-> False
list1 + list2
-> [123,456,234,345]
list1 * 2
-> [123,456,123,456]
456 in list1
-> True
456 not in list1
-> Falsse
list3 = [1,2,[3,4]]
3 in list3
-> False
3 in list3[2]
-> True
list3[2][1]
-> 4
21. In python , how many method of list
we can use dir(list) to find out it
now i show some common method:
a = [12, 13, 13, 14]
a.count(13)
-> 2
a.index(14)
-> 3
a.reverse()
-> [14, 13, 13, 13]
b = [2, 1, 3 ,5, 4]
b.sort()
-> [1, 2, 3, 4, 5]
b.sort(reverse = True)
-> [5, 4, 3, 2, 1]
22. In python , there are also have an important type tuple
if you define a tuple , you can't change it , but if it is list ,you can modify ,insert ,delete value.
now that we have list , why we need tuple , i guess , they are like array and mutablearray in oc.
tuple1 = (1,2,3,4,5,6,7)
tuple1[1]
-> 2
tuple1[:]
-> (1,2,3,4,5,6,7)
but we can't modify it , such as:
tuple1[1] = 10
-> error
now we can some special thing :
temp = (1)
-> 1
type(temp)
-> int
temp = 1, 2
type(temp)
-> tuple
so if tuple is one number , we should user temp = (1,) or temp = 1, then type(temp) can get tuple
now we can see an interesting question:
6 * (6) -> 36
6 * (6,) -> (6, 6, 6, 6, 6, 6)
how to add a new value to duple:
such as:
temp = ('roy' ,'wyg' ,'tom')
temp = temp[:2] + ('jim',) + temp[2:]
-> ('roy' ,'wyg', 'jim' ,'tom')
we can use del temp to delete all temp
duple we can user + , * , = , in , not in , and , or etc.
23. In python , str is an important type. it is similar to duple.
str1 = 'my name is roy'
str1[:6]
-> 'my nam'
str1[3]
-> n
str1[:6] + 'ttt' + str1[6:]
-> 'my namttte is roy'
str2 = 'roy'
str2.capitalize()
-> 'Roy'
str3 = 'ROY'
str3.casefold()
-> 'roy'
str4 = 'roy'
str4.center(6)
-> ' roy '
str5 = 'royroy'
str5.count('y')
-> 2
str6 = 'roy'
str6.endswith('oy')
-> True
str7 = 'I\tlove\tyou'
str7.expandtabs()
-> 'I love you'
str8 = 'abcd'
str8.find('d')
-> 3
str8.find('e')
-> -1
str8.index('d')
-> 3
str8.index('e')
-> error
there are also other method:
isalnum() #如果字符串中至少有一个字符并且所有字符都是字母或数字返回True
isalpha() #如果字符串中至少有一个字符并且所有字符都是字母返回True
isdecimal()#如果字符串只包含十进制数字返回True
isdigit() ＃如果字符串中只包含数字返回True
islower() ＃如果字符串中至少包含一个区分大小写的字符，并且这些字符都是小写，返回True
isnumeric() #如果字符串中只包含数字字符，返回True
isspace() #如果字符串中只包含空格，返回True
istitle() #如果字符串是标题化，所有单词大写开始，其余小写，返回True
isupper() #如果字符串中至少包含一个区分大小写的字符，并且这些字符都是大写，返回True
lstrip() #去掉字符串中左边所有空格
rstrip() #去掉字符串右边所有空格
join(sub) #以字符串作为分隔符，插入到sub中所有的字符之间
ljust(width) #返回一个左对齐字符串，并使用空格填充至width长度
lower() #大写字符转化为小写
partition(sub) #找到子字符串sub,把字符串分割一个3元组，如不包含sub,则返回元字符串
replace(old,new[,count]) #把old换成new，如果count指定，则替换不超过count次
rfind(sub,[,start,[,end]) #类find，从右边开始查找
rindex(sub,[,start],[,end]) #类index，从右边开始
rpartition(sub) #类似partition(),从右边开始查找
rjust(width) #右对齐
split(sep = None,maxsplit = -1) #不带参数是以空格为分隔符，如maxsplit有设置，则分割成maxsplit个子字符串，返回列表
splitlines(([keepends])) #按照\n分隔，返回一个包含各行作为元素的列表，如制定keepends，返回前keepends行
swapcase() #翻转字符串中的大小写
title() #返回标题话
startswith(prefix[,start][,ends]) ＃是否以prefix开始，返回 True
strip(［chars]) #删除字符串前边和后边所有空格
upper()
translate(table) #替换字符
zfil(width) #右边对齐，前边0填充
