String concatenation
Actual scene: the data list together into a string
Solution: Use str.join () method
>>> li = ['cxk', 'cxk', 'kk', 'caibi']
>>> ''.join([str(i) for i in li])
'cxkcxkkkcaibi'
We recommended to use a generator expression, if the list is large, you can save a lot of memory space
>>> ''.join(str(i) for i in li)
'3cxkkkcaibi'
Split string delimiter contains a variety of
The actual scene of: dividing a character string based on different symbol splitter field, the string comprising a plurality of different delimiter
s = "ab;fd/ft|fs,f\tdf.fss*dfd;fs:uu}fsd"
1. The python split () method, a processing time since the split separator, for example:
>>> res = s.split(';')
>>> res
['ab', 'fd/ft|fs,f\tdf.fss*dfd', 'fs:uu}fsd']
So we need to string delimiter sequence segmentation may be a map function!
>>> list(map(lambda x: x.split("|"), res))
[['ab'], ['fd/ft', 'fs,f\tdf.fss*dfd'], ['fs:uu}fsd']]
The results turned into a two-dimensional list, and the result we want is one-dimensional list, how do?
Create a temporary list to save the results.
'''
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'''
>>> t = []
>>> list(map(lambda x: t.extend(x.split("|")), res))
[None, None, None]
>>> t
['ab', 'fd/ft', 'fs,f\tdf.fss*dfd', 'fs:uu}fsd']
The results met our expectations! Then continue processing the rest of the separator, the operation is repeated, for loop get!
The final code is as follows:
def my_split(s, ds):
res = [s]
for d in ds:
t = []
list(map(lambda x: t.extend(x.split(d)), res))
res = t
return res
The string and the string delimiters all incoming following results:
s = "ab;fd/ft|fs,f\tdf.fss*dfd;fs:uu}fsd"
print(my_split(s, ";/|,.}:*\t"))
运行结果：['ab', 'fd', 'ft', 'fs', 'f', 'df', 'fss', 'dfd', 'fs', 'uu', 'fsd']
2. re module split () method
re () also provides us with the split () method, can be a one-time-delimited string!
import re
s = "ab;fd/ft|fs,f\tdf.fss*dfd;fs:uu}fsd"
print(re.split('[;/|,.}:*\t]', s))
Results are consistent, it is not very simple and crude!
Interpretation of a string of whether the beginning or end of the string b
actual scene: for example, there is a series of files in a directory:
Write a program to which all .txt files and executable .py file with user rights
solution:
String str.startswith () and str.endswith ()
And find a .txt ending .py file that accepts a tuple
>>> import os
>>> os.listdir(".")
['app', 'config', 'requirements.txt', 'run.py', '__pycache__', 'gunicorn.conf.py', 'chromedriver', 'login_after2.png', 'readme.txt', 'slide.png', 'test.py', 'logs', 'chrome-linux.zip', 'gunicorn.pid', 'asgi.py', 'chrome-linux']
>>> [name for name in os.listdir(".") if name.endswith((".txt", ".py"))]
['requirements.txt', 'run.py', 'gunicorn.conf.py', 'readme.txt', 'test.py', 'asgi.py']
Chinese string format adjustment according to the present
Actual text column: for example, in a log file, where the date format is 'yyyy-mm-dd':
We want to change the date in which the US date format 'mm / dd / yyyy'. For example 2019-06-12 06/12/2019 format into
Solution: Use of re sub () method to do the replacement string
Regular expressions in the capture group, capturing the contents of each part, and then replace the order of the respective adjustment groups captured string alternative!
code show as below:
'''
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'''
import re
with open("info.log", "r", encoding="utf-8") as f:
file = f.read()
print(re.sub('(\d{4})-(\d{2})-(\d{2})', r'\2/\3/\1', file))
Capturing each group need parentheses, and then from left to right by default into groups 1, 2 ...
The next parameter is the format we want to replace, respectively, with 1,2,3 groups 1, 2 ...
Results are as follows:
The string left, right, center alignment
solution:
1. string str.ljust (), str.rjust (), str.center () for about centered!
Basic usage above three methods:
>>> s = 'abc'
>>> s.ljust(20, '=')
'abc================='
>>> s.ljust(20)
'abc '
All three methods can set default values to fill
2. Use the built-in format () method
>>> format(s, ">20")
' abc'
>>> format(s, "<20")
'abc '
>>> format(s, "^20")
' abc '
Delete unwanted characters in the string
actual case:
Filter out the excess before and after the user enters a blank character: "[email protected]"
Editing text filter out some windows at the "\ r": "hello world \ r \ n"
unicode combined symbol text removed (pitch): nǐ hǎo mā
solution:
Use str.strip (), str.lstrip (), str.rstrip () method to remove the character string ends
Use str.replace () or regular in the re.sub ()
Use string str.translate () method, a plurality of different characters can be deleted at the same time