Meet Python: little notes

Source: http://www.liaoxuefeng.com/

 

❤ Escape character: '\'

- '\n': newline;

- '\t': tab;

- '\\': \;

- r'...': no transferring for contents within single quotes;

- '''...''': multiple lines within triple quotes: could start a new line with ENTER directly. r'''...''' is valid as well.

 

❤ Division

- '/': floating point calculation, alway return float;

- '//': only return integer part (decimal part is direclty abandoned);

- '%': return remainder.

 

❤ Character encoding

- Encoding standard

    .. ASCII: some symbold, number, uppercase and lowercase, 1 byte representing 1 character;

    .. GB2312: Chinese character;

    .. Unicode: encoding characters in all languages using one criterion, 2 bytes representing 1 character usually;

    .. UTF-8: to save space, converting Unicode into 1-6 bytes (usually, one English character: 1 bytes, while one Chinses: 3 bytes); criterion used in RAM;

- Python

    .. encoding using unicode;

    .. for sigle character, ord() - obtaining integral representing for the character; chr() - converting code into character;

    .. b'...': converting string to byte format (one byte fot each character);

    .. '...'.encode('method'): encode ... using corresponding method('ascii', 'utf-8', note that Chinese characters cannot be encoded using 'ascii');

    .. b'...'.decode('method'): decode byte string '...' into characters using corredponding method ('ascii', 'utf-8');

    .. len('...'): obtain number of characters or bytes in '...';

    .. formatting characters: the same way as c (and matlab :p):

          %s - character string;

          %d: integer;

          %f: floating;                                                    

          %x: hexadecimal integer.

       some examples:

>>> 'Hello, %s' % 'world'
'Hello, world'

>>> 'Hi, %s, you have $%d.' % ('Michael', 1000000)
'Hi, Michael, you have $1000000'.

>>> '%2d-%02d' % (3, 1)
'3-01'
>>> '%.2f' % 3.1415
'3.14'

>>> 'Age: %s; Gender: %s' % (25, True)   # If you cannot decide which placeholder to use, just use %s
'Age: 25; Gender: true'

>>> 'Growth rate: %d %%' % 7
'Growth rate: 7 %'

 

NOTE: we should stick to 'utf-8' for converting to avoid chaos, to ensure which: 1. make sure your text editor is using: "UTF-8 without BOM" as encoding methods; 2. add the following two lines at the beginning of your script.

#!/usr/bin/env python3
# -*- coding: utf-8 -*-