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