Python f-string有没有一种简单的方法来固定小数点后的位数?(特别是f-string,而不是.format或%等其他字符串格式选项)
例如,假设我想在小数点后显示2位数字。
我该怎么做?让我们这么说吧
a = 10.1234
Python f-string有没有一种简单的方法来固定小数点后的位数?(特别是f-string,而不是.format或%等其他字符串格式选项)
例如,假设我想在小数点后显示2位数字。
我该怎么做?让我们这么说吧
a = 10.1234
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'
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:,}$')
I am worth 10,000,000,000$
a = 10.1234
print(f"{a:0.2f}")
在0.2f中:
0告诉python不限制陈列.2表示我们只想在小数后取2位(结果将与round()函数相同)f表示它是一个浮点数。如果你忘记了f,那么它只会在小数点后少打印1个数字。在这种情况下,它只能是小数后1位。
关于数字f-string的详细视频https://youtu.be/RtKUsUTY6to?t=606
>>> 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
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" | "%"
参考https://docs.python.org/3/library/string.html#format-字符串语法
仅仅
a = 10.1234
print(f"{a:.1f}")
输出:10.1
a = 10.1234
print(f"{a:.2f}")
输出:10.12
a = 10.1234
print(f"{a:.3f}")
输出:10.123
a = 10.1234
print(f"{a:.4f}")
输出:10.1234
只需更改小数点符号后的值,小数点符号表示您要打印的小数点。
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
参考:其他SO答案