How to use python's format

How to use python’s format?

Python’s format function usage

It enhances the string formatting function. The basic syntax is to replace the previous % with {} and :. The format function can accept unlimited parameters, and the positions do not need to be in order.

**Example 1: The **format function can accept unlimited parameters, and the positions do not need to be in order.

"{} {}".format("hello", "world")    # 不设置指定位置，按默认顺序
运行结果：'hello world'
 "{0} {1}".format("hello", "world")  # 设置指定位置
运行结果：'hello world'
"{1} {0} {1}".format("hello", "world")  # 设置指定位置
运行结果：'world hello world'

Example 2: You can also set parameters.

print("网站名：{name}, 地址 {url}".format(name="Python教程", url="www.py.cn"))
# 通过字典设置参数
site = {"name": "Python教程", "url": "www.py.cn"}
print("网站名：{name}, 地址 {url}".format(**site))
# 通过列表索引设置参数
my_list = ['Python教程', 'www.py.cn']
print("网站名：{0[0]}, 地址 {0[1]}".format(my_list))  # "0" 是必须的
运行结果：
网站名：Python教程, 地址 www.py.cn
网站名：Python教程, 地址 www.py.cn
网站名：Python教程, 地址 www.py.cn

Example 3: You can also pass in the object to str.format():

class AssignValue(object):
    def __init__(self, value):
        self.value = value
my_value = AssignValue(6)
print('value 为: {0.value}'.format(my_value))  # "0" 是可选的

The output result is:

value 为: 6

Example 4: The following table shows str.format () Multiple methods of formatting numbers

print("{:.2f}".format(3.1415926));
3.14

Number formatting methods

Number format output description

3.1415926 {:.2f} 3.14 Keep two decimal places

3.1415926 {: .2f} 3.14 Signed to two decimal places

-1 {: .2f} -1.00 Signed to two decimal places

2.71828 {:. 0f} 3 without decimal

5 {:0>2d} 05 Numeric zero padding (padding to the left, width is 2)

5 {:x<4d} 5xxx Numerical padding x (padding Right side, width is 4)

10 {:x<4d} 10xx number complement

##0.25 {:.2%} 25.00% Percent format

1000000000 {:.2e} 1.00e 09 Exponent notation

13 {:10d} 13 Right justified (default , width is 10)

13 {:<10d} 13 left-aligned (width is 10)

13 {:^10d} 13 center-aligned (width is 10)

'{:b}'.format(11) 1011

'{:d}'.format(11) 11

11's base '{:o}'.format (11) 13

'{:x}'.format(11) b

'{:#x}'.format(11) 0xb

'{: #X}'.format(11) 0XB

^, <, > are centered, left-aligned, and right-aligned respectively, followed by width, followed by : and filled with characters, which can only be one character , if not specified, it will be filled with spaces by default.

means displaying before positive numbers and - before negative numbers; (space) means adding spaces before positive numbers

b, d, o, x are binary, decimal, octal, and ten respectively Hexadecimal.

Example 5:

Give you a dictionary:

t={‘year’:’2013’,’month’:’9’,’day’:’30’,’hour’:’16’,’minute’:’45’,’second’:’2’}

Please output in this format: 2013-09-30 16:45:02

def data_to_str(d):
    '''
    :param d: 日期字典
    :return: str 格式化后的日期
    '''
    s1='{} {:>02} {:>02}'.format(t['year'],t['month'],t['day'])
    s2='{} {:>02} {:>02}'.format(t['hour'],t['minute'],t['second'])
    print(s1,s2)
    print('-'.join(s1.split()),end=' ')
    print(':'.join(s2.split()))
    return 0
t={'year':'2013','month':'9','day':'30','hour':'16','minute':'45','second':'2'}
print(data_to_str(t))

Run results:

2013 09 30 16 45 02
2013-09-30 16:45:02

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