Python Learning notes-Little Kee

1. Strings String

Infer whether a character (char) is a number or a letter

#推断是否为字母#推断是否为数字

Infer whether a string is empty

ifnot#推断是否为空，true表示空

Adding content to a string

‘‘.join(‘love‘)

Get string fixed-length strings

>>>str = str1[1:3#得到从下标1開始到下标3之前的字符，下标3的字符不算

String substitution

>>>str.replace(‘abc‘,‘cde‘)

2. List of lists

Infer if a list is empty

>>>if len(lists):   #true表示空#向列表中加入数据>>>lists.append(‘1‘)#得到list某个值的下标>>>lists.index(‘1‘)

3. File Operation

Read the file

>>>with open(‘filename‘,‘r‘as f1:

Write a file

>>>with open(‘filename‘,‘w‘as f2:>>> ......>>> f2.write(‘my name is ldw.‘)

Get the entire folder file

>>>import os>>>files = os.listdir("/ifs/home/liudiwei")>>>forin files:    #onefile即递归得到的每一个文件>>> ...               

To infer whether the current folder exists and does not exist to create a folder:

ifnotos.path.exists(outdir): #假设outdir不存在，则创建该文件夹        os.makedirs(outdir)

Python runs the current system command

os.system(‘[command]‘)  #command为想要运行的命令

4. Collection Operations

Create a Collection

s = set(‘thisisset‘)

adding elements

s.add(‘z‘)

Set length

len(s)

Inferred Collection Non-empty

iflen(s):   #假设长度为0，返回false

Infer that a collection has an element

‘k‘in s    #或者能够是 ‘k‘ not in s

Recycling elements

del s

5. Floating-point Division

Set A and B as two integers. Dividing two numbers requires floating-point results

c=float(a)/float(b)

If you need to keep decimals

c=float(‘%.3f‘float(a)/float(b))

6. Building an array

Generates an array of 8000*4 matrices

 def Genmatrix():aa=[' A ',' C ',' D ',' E ',' F ',' G ',' H ',' I ',' K ',' L ',' M ',' N ',' P ',' Q ',' R ',' S ',' T ',' V ',' W ',' Y ',] triplet = [] forIinchRange (len (AA)): forJinchRange (len (AA)): forKinchRange (len (AA)): Triplet.append (Aa[i]+aa[j]+aa[k]) rna=[' A ',' U ',' G ',' C '] Matrix = [[0  forColinchRange (len (RNA))] forRowinchRange (len (triplet))]returnTriplet,rna,matrix'

7. Dictionaries

Python dictionaries are more useful, similar to maps in java/c++. Key-value pairs. In practice, Python can find value based on the key.
Defined

dict_map = {}#赋值dict_map[‘number‘2#查看是否存在某个键dict_map.has_key(‘number‘)#if exist, return True,else return False

Python Learning notes-Little Kee