似乎没有人使用动态格式化程序。要使用动态格式化程序，请使用：

WIDTH = 7
PRECISION = 3
TYPE = "f"

v = 3
print(f"val = {v:{WIDTH}.{PRECISION}{TYPE}}")

其他格式请参见：https://docs.python.org/3.6/library/string.html#format-规范小型语言

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参考：其他SO答案

添加到Robᵩ's回答：如果你想打印相当大的数字，使用千个分隔符可以是一个很大的帮助（注意逗号）。

>>> f'{a*1000:,.2f}'
'10,123.40'

如果您想填充/使用固定宽度，则宽度在逗号之前：

>>> f'{a*1000:20,.2f}'
'           10,123.40'

当涉及浮点数时，可以使用格式说明符：

f'{value:{width}.{precision}}'

哪里：

value是计算结果为数字的任何表达式width指定要显示的字符总数，但如果value需要的空间大于width指定的空间，则使用额外的空间。precision表示小数点后使用的字符数

缺少的是十进制值的类型说明符。在此链接中，您可以找到浮点和小数的可用表示类型。

这里有一些使用f（固定点）表示类型的示例：

# notice that it adds spaces to reach the number of characters specified by width
In [1]: f'{1 + 3 * 1.5:10.3f}'
Out[1]: '     5.500'

# notice that it uses more characters than the ones specified in width
In [2]: f'{3000 + 3 ** (1 / 2):2.1f}' 
Out[2]: '3001.7'

In [3]: f'{1.2345 + 4 ** (1 / 2):9.6f}'
Out[3]: ' 3.234500'

# omitting width but providing precision will use the required characters to display the number with the the specified decimal places
In [4]: f'{1.2345 + 3 * 2:.3f}' 
Out[4]: '7.234'

# not specifying the format will display the number with as many digits as Python calculates
In [5]: f'{1.2345 + 3 * 0.5}'
Out[5]: '2.7344999999999997'

添加到Rob的答案中，您可以将格式说明符与f字符串一起使用（这里有更多）。

您可以控制小数位数：

pi = 3.141592653589793238462643383279

print(f'The first 6 decimals of pi are {pi:.6f}.')

The first 6 decimals of pi are 3.141593.

您可以转换为百分比：

grade = 29/45

print(f'My grade rounded to 3 decimals is {grade:.3%}.')

My grade rounded to 3 decimals is 64.444%.

您可以执行其他操作，如打印恒定长度：

from random import randint
for i in range(5):
    print(f'My money is {randint(0, 150):>3}$')

My money is 126$
My money is   7$
My money is 136$
My money is  15$
My money is  88$

或甚至使用逗号千分隔符打印：

print(f'I am worth {10000000000:,}$')

I am worth 10,000,000,000$

在格式表达式中包含类型说明符：

>>> a = 10.1234
>>> f'{a:.2f}'
'10.12'

Consider:

>>> number1 = 10.1234
>>> f'{number1:.2f}'
'10.12'

Syntax:

"{" [field_name] ["!" conversion] [":" format_spec] "}"

Explanation:

# Let's break it down...
#       [field_name]     => number1
#       ["!" conversion] => Not used
#       [format_spec]    => [.precision][type] 
#                        => .[2][f] => .2f  # where f means Fixed-point notation

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更进一步，Format字符串具有以下语法。正如你所看到的，还有很多事情可以做。

Syntax: "{" [field_name] ["!" conversion] [":" format_spec] "}"

# let's understand what each field means...
    field_name        ::=  arg_name ("." attribute_name | "[" element_index "]")*
    arg_name          ::=  [identifier | digit+]
    attribute_name    ::=  identifier
    element_index     ::=  digit+ | index_string
    index_string      ::=  <any source character except "]"> +
    conversion        ::=  "r" | "s" | "a"
    format_spec       ::=  [[fill]align][sign][#][0][width][grouping_option][.precision][type]

            # Looking at the underlying fields under format_spec...
            fill            ::=  <any character>
            align           ::=  "<" | ">" | "=" | "^"
            sign            ::=  "+" | "-" | " "
            width           ::=  digit+
            grouping_option ::=  "_" | ","
            precision       ::=  digit+
            type            ::=  "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "s" | "x" | "X" | "%"

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参考https://docs.python.org/3/library/string.html#format-字符串语法