Notes on Python cookbook 3rd (2.14): merging and splicing strings

Giant ship 2020-11-14 01:02:14
notes python cookbook 3rd rd


Merge concatenated strings

problem

You want to combine several small strings into one big string

solution

If the string you want to merge is in a sequence or iterable in , So the fastest way is to use join() Method . such as :

>>> parts = ['Is', 'Chicago', 'Not', 'Chicago?']
>>> ' '.join(parts)
'Is Chicago Not Chicago?'
>>> ','.join(parts)
'Is,Chicago,Not,Chicago?'
>>> ''.join(parts)
'IsChicagoNotChicago?'
>>>

First look , It looks strange , however join() A method specified as a string . Part of the reason for this is that the objects you want to connect to may come from a variety of different data sequences ( Such as the list , Tuples , Dictionaries , file , Set or generator, etc ), If you define one on all of these objects join() The method is obviously redundant . So you just need to specify the split string you want and call it join() Method to combine text fragments .


If you just merge a few strings , Use the plus sign (+) Usually enough :

>>> a = 'Is Chicago'
>>> b = 'Not Chicago?'
>>> a + ' ' + b
'Is Chicago Not Chicago?'
>>>

plus (+) The operator also works well as an alternative to some complex string formatting , such as :

>>> print('{} {}'.format(a,b))
Is Chicago Not Chicago?
>>> print(a + ' ' + b)
Is Chicago Not Chicago?
>>>

If you want to merge two literal strings in the source code , You just need to simply put them together , There's no need to use the plus sign (+). such as :

>>> a = 'Hello' 'World'
>>> a
'HelloWorld'
>>>

Discuss

The programmer usually brings serious performance loss to the application due to improper selection when formatting strings .

The most important thing to notice is , When we use the plus sign (+) Operators are very inefficient to join a large number of strings , Because plus connection will cause memory copy and garbage collection operation . Special , You should never write string concatenation code like this :

s = ''
for p in parts:
s += p

This way of writing is better than using join() The method runs slower , Because every execution += Operation will create a new string object . You'd better collect all the string fragments first and then connect them .

A relatively clever trick is to use generator expressions to convert data into strings while merging strings , such as :

>>> data = ['ACME', 50, 91.1]
>>> ','.join(str(d) for d in data)
'ACME,50,91.1'
>>>

Also pay attention to unnecessary string concatenation operations . Sometimes a programmer does not have to do a connection operation when it is unnecessary to do so . For example, when printing :

print(a + ':' + b + ':' + c) # Ugly
print(':'.join([a, b, c])) # Still ugly
print(a, b, c, sep=':') # Better

When mixed with I/O Operations and string concatenation operations , Sometimes you need to study your program carefully . such as , Consider the following two end code snippets :

# Version 1 (string concatenation)
f.write(chunk1 + chunk2)
# Version 2 (separate I/O operations)
f.write(chunk1)
f.write(chunk2)

If two strings are very small , Then the performance of the first version will be better , because I/O System calls are inherently slow . On the other hand , If two strings are large , So the second version might be more efficient , Because it avoids creating a large temporary result and copying a lot of memory block data . Or that sentence , Sometimes it's up to you to decide which solution to use based on the characteristics of your application .

Finally, let's talk about it , If you're going to write output code that builds a lot of small strings , You'd better consider using generator functions , utilize yield Statement produces output fragments . such as :

def sample():
yield 'Is'
yield 'Chicago'
yield 'Not'
yield 'Chicago?'

One interesting aspect of this approach is that it doesn't make assumptions about how the output fragment should be organized . for example , You can simply use join() Methods combine these fragments together :

text = ''.join(sample())

Or you can redirect string fragments to I/O:

for part in sample():
f.write(part)

Or you can also write some combinations I/O A hybrid scheme of operations :

def combine(source, maxsize):
parts = []
size = 0
for part in source:
parts.append(part)
size += len(part)
if size > maxsize:
yield ''.join(parts)
parts = []
size = 0
yield ''.join(parts)

# Combined with file operation 
with open('filename', 'w') as f:
for part in combine(sample(), 32768):
f.write(part)
版权声明
本文为[Giant ship]所创,转载请带上原文链接,感谢

  1. 利用Python爬虫获取招聘网站职位信息
  2. Using Python crawler to obtain job information of recruitment website
  3. Several highly rated Python libraries arrow, jsonpath, psutil and tenacity are recommended
  4. Python装饰器
  5. Python实现LDAP认证
  6. Python decorator
  7. Implementing LDAP authentication with Python
  8. Vscode configures Python development environment!
  9. In Python, how dare you say you can't log module? ️
  10. 我收藏的有关Python的电子书和资料
  11. python 中 lambda的一些tips
  12. python中字典的一些tips
  13. python 用生成器生成斐波那契数列
  14. python脚本转pyc踩了个坑。。。
  15. My collection of e-books and materials about Python
  16. Some tips of lambda in Python
  17. Some tips of dictionary in Python
  18. Using Python generator to generate Fibonacci sequence
  19. The conversion of Python script to PyC stepped on a pit...
  20. Python游戏开发,pygame模块,Python实现扫雷小游戏
  21. Python game development, pyGame module, python implementation of minesweeping games
  22. Python实用工具,email模块,Python实现邮件远程控制自己电脑
  23. Python utility, email module, python realizes mail remote control of its own computer
  24. 毫无头绪的自学Python,你可能连门槛都摸不到!【最佳学习路线】
  25. Python读取二进制文件代码方法解析
  26. Python字典的实现原理
  27. Without a clue, you may not even touch the threshold【 Best learning route]
  28. Parsing method of Python reading binary file code
  29. Implementation principle of Python dictionary
  30. You must know the function of pandas to parse JSON data - JSON_ normalize()
  31. Python实用案例,私人定制,Python自动化生成爱豆专属2021日历
  32. Python practical case, private customization, python automatic generation of Adu exclusive 2021 calendar
  33. 《Python实例》震惊了,用Python这么简单实现了聊天系统的脏话,广告检测
  34. "Python instance" was shocked and realized the dirty words and advertisement detection of the chat system in Python
  35. Convolutional neural network processing sequence for Python deep learning
  36. Python data structure and algorithm (1) -- enum type enum
  37. 超全大厂算法岗百问百答(推荐系统/机器学习/深度学习/C++/Spark/python)
  38. 【Python进阶】你真的明白NumPy中的ndarray吗?
  39. All questions and answers for algorithm posts of super large factories (recommended system / machine learning / deep learning / C + + / spark / Python)
  40. [advanced Python] do you really understand ndarray in numpy?
  41. 【Python进阶】Python进阶专栏栏主自述:不忘初心,砥砺前行
  42. [advanced Python] Python advanced column main readme: never forget the original intention and forge ahead
  43. python垃圾回收和缓存管理
  44. java调用Python程序
  45. java调用Python程序
  46. Python常用函数有哪些?Python基础入门课程
  47. Python garbage collection and cache management
  48. Java calling Python program
  49. Java calling Python program
  50. What functions are commonly used in Python? Introduction to Python Basics
  51. Python basic knowledge
  52. Anaconda5.2 安装 Python 库(MySQLdb)的方法
  53. Python实现对脑电数据情绪分析
  54. Anaconda 5.2 method of installing Python Library (mysqldb)
  55. Python implements emotion analysis of EEG data
  56. Master some advanced usage of Python in 30 seconds, which makes others envy it
  57. python爬取百度图片并对图片做一系列处理
  58. Python crawls Baidu pictures and does a series of processing on them
  59. python链接mysql数据库
  60. Python link MySQL database