Shulou(Shulou.com)06/03 Report--

This article mainly explains "what is the use of Pythonic". The content of the explanation is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "what is the use of Pythonic"?

1. Variable exchange

If you exchange the values of two variables, you will normally want to use an intermediate temporary variable to transition.

Tmp = an a = b b = tmp

If it can be solved with one line of code (and does not affect readability), never use three lines of code.

A _

two。 List derivation

Here is a very simple for loop.

My_list = [] for i in range (10): my_list.append (iTun2)

In a for loop, if the logic is simple, try the list derivation of the list, which has only one line of code, but the logic is clear.

My_list = [iTun2 for i in range (10)]

3. One-line expression

In both cases, multiple lines of code are written into one line of code in another way.

This does not mean that the fewer lines of code, the more Pythonic.

For example, if it is written like this, it is not recommended.

Print ('hello'); print (' world') if x = = 1: print ('hello,world') if and: # do something

The suggestion is to write as follows.

Print ('hello') print (' world') if x = = 1: print ('hello,world') cond1 = cond2 = if cond1 and cond2: # do something

4. Indexed traversal

When using for loop, how to get the corresponding index? beginners are used to using range + len function.

For i in range (len (my_list)): print (I, "-->", my_ list [I])

A better approach is to use enumerate as a built-in function

For iMart item in enumerate (my_list): print (I, "-->", item)

5. Sequence unpacking

Use * to unpack a list

A, * rest = [1,2,3] # a = 1, rest = [2,3] a, * middle, c = [1,2,3,4] # a = 1, middle = [2,3], c = 4

6. String concatenation

If all elements in a list (or iterable object) are string objects, it is common practice to concatenate them

Letters = ['for let in letters,' paired, 'ajar,' m'] s = "" for let in letters: s + = let

A more recommended approach is to use the join function

Letters = ['s cause, 'pause,' asides,'m'] word = '.join (letters)

7. True or false judgment

To judge whether a variable is true (false), beginners are accustomed to directly using = = to compare with True, False and None.

If attr = = True: print ('truth') If attr = = None: print ('attr is nonprofit')

In fact, containers without any elements, such as "", [], {}, are false values and can be judged directly using if not xx.

If attr: print ('attr is truthful') If not attr: print ('attr is false')

8. Access dictionary elements

When you directly use [] to access the elements in the dictionary, if the key does not exist, an exception will be thrown, so the new association may first determine whether there is this key and then take it.

D = {'hello':' world'} if d.has_key ('hello'): print (d [' hello']) # prints' world' else: print ('default_value')

It is more recommended to use get to fetch it. If there is no such key, None will be returned by default (of course, you can also set the default return value)

D = {'hello':' world'} print (d.get ('hello',' default_value')) # prints' world' print (d.get ('thingy',' default_value')) # prints' default_value'

9. Operation list

The following code filters the elements in the list based on conditions

A = [3,4,5] b = [] for i in a: if I > 4: b.append (I)

It can actually be implemented using list derivation or higher-order function filter.

A = [3,4,5] b = [i for i in an if i > 4] # Or: B = filter (lambda x: X > 4, a)

In addition to filter, map and reduce are also easy to use.

A = [3,4,5] b = map (lambda I: I + 3, a) # b: [6, 7, 8]

10. File reading

File reading is a very common operation. After using the handle, you need to manually call the close function to close the handle.

Fp = open ('file.txt') print (fp.read ()) fp.close ()

If the code is too long, you will often miss it, even if you know you need to close the handle manually. Therefore, it is recommended to get into the habit of using with open to read and write files, and the context manager will automatically close the handle.

With open ('file.txt') as fp: for line in fp.readlines (): print (line)

11. Code continuation

Putting a long string on one line can affect the readability of the code (the following code can slide to the left)

Long_string = 'For a long time I used to go to bed early. Sometimes, when I had put out my candle, my eyes would close so quickly that I had not even time to say "I'm going to sleep."'

Those who pay attention to the readability of the code will use three quotation marks to continue the writing.

Long_string = 'For a long time I used to go to bed early.'\ 'Sometimes, when I had put out my candle,'\'my eyes would close so quickly that I had not even time to say "I'm going to sleep."

However, for me, I prefer to write this way and wrap it in parentheses ()

Long_string = ("For a long time I used to go to bed early. Sometimes,"when I had put out my candle, my eyes would close so quickly"that I had not even time to say" I'm going to sleep. "")

The same is true when guiding the bag.

From some.deep.module.inside.a.module import (a_nice_function, another_nice_function, yet_another_nice_function)

twelve。 Explicit code

Sometimes, out of necessity, we use some special magic to adapt the code to more scenario uncertainty.

Def make_complex (* args): X, y = args return dict (* * locals ())

But please don't do that if it's not necessary. Increasing the uncertainty of the code for no reason will make the already dynamic language write more dynamic code.

Def make_complex (x, y): return {"x": X, "y": y}

13. Use placeholders

For variables that are not needed but have to be accepted, use placeholders

Filename = 'foobar.txt' basename, _, ext = filename.rpartition ('.')

14. Chain comparison

For the following way of writing

Score = 85 if score > 80 and score

> > False = = False = = True False

15. Trinocular operation

For simple judgment and assignment

Age = 20 if age > 18: type = "adult" else: type = "teenager"

In fact, you can use trinomial operation to do it in one line.

Age = 20b = "adult" if age > 18 else "teenager" Thank you for your reading, the above is the content of "what is the use of Pythonic?" after the study of this article, I believe you have a deeper understanding of the use of Pythonic, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.