Python 字符串 format() 方法
Python基础 2022-06-06 15:20:27小码哥的IT人生shichen
Python 字符串 format() 方法
实例
将价格插入占位符内，价格应为定点，两位十进制格式：
txt = "For only {price:.2f} dollars!"
print(txt.format(price = 49))
完整实例：
txt = "For only {price:.2f} dollars!"
print(txt.format(price = 49))定义和用法
format() 方法格式化指定的值，并将其插入字符串的占位符内。
占位符使用大括号 {} 定义。请在下面的“占位符”部分中了解有关占位符的更多信息。
format() 方法返回格式化的字符串。
语法
string.format(value1, value2...)
参数值
| 参数 | 描述 |
|---|---|
| value1, value2... |
必需。一个或多个应该格式化并插入字符串的值。值可以是数字，用于指定要删除的元素的位置。 这些值可以是用逗号分隔的值列表、键=值列表，或两者的组合。 这些值可以是任何数据类型。 |
占位符
可以使用命名索引 {price}、编号索引{0}、甚至空的占位符 {} 来标识占位符。
示例代码：
使用不同的占位符值：
txt1 = "My name is {fname}, I'am {age}".format(fname = "Bill", age = 64)
txt2 = "My name is {0}, I'am {1}".format("Bill",64)
txt3 = "My name is {}, I'am {}".format("Bill",64)
完整实例：
#named indexes:
txt1 = "My name is {fname}, I'm {age}".format(fname = "Bill", age = 63)
#numbered indexes:
txt2 = "My name is {0}, I'm {1}".format("Bill",63)
#empty placeholders:
txt3 = "My name is {}, I'm {}".format("Bill",63)
print(txt1)
print(txt2)
print(txt3)
格式化类型
在占位符内，您可以添加格式化类型以格式化结果：
| :< | 试一试 | 左对齐结果（在可用空间内） |
| :> | 试一试 | 右对齐结果（在可用空间内） |
| :^ | 试一试 | 居中对齐结果（在可用空间内） |
| := | 试一试 | 将标志放置在最左侧 |
| :+ | 试一试 | 使用加号指示结果是正数还是负数 |
| :- | 试一试 | 负号仅用于负值 |
| : | 试一试 | 使用空格在正数之前插入一个多余的空格（在负数之前使用减号） |
| :, | 试一试 | 使用逗号作为千位分隔符 |
| :_ | 试一试 | 使用下划线作为千位分隔符 |
| :b | 试一试 | 二进制格式 |
| :c | 将值转换为相应的 unicode 字符 | |
| :d | 试一试 | 十进制格式 |
| :e | 试一试 | 科学格式，带有小写字母 E |
| :E | 试一试 | 科学格式，带有大写字母 E |
| :f | 试一试 | 定点数字格式 |
| :F | 试一试 | 定点数字格式，以大写形式显示（将 inf 和 nan 显示为 INF 和 NAN） |
| :g | 通用格式 | |
| :G | 通用格式（将大写 E 用作科学计数法） | |
| :o | 试一试 | 八进制格式 |
| :x | 试一试 | 十六进制格式，小写 |
| :X | 试一试 | 十六进制格式，大写 |
| :n | 数字格式 | |
| :% | 试一试 | 百分比格式 |
完整实例1：
#To demonstrate, we insert the number 8 to set the available space for the value to 8 characters.
#Use ">" to right-align the value:
txt = "We have {:>8} chickens."
print(txt.format(49))完整实例2：
#To demonstrate, we insert the number 8 to set the available space for the value to 8 characters.
#Use "^" to center-align the value:
txt = "We have {:^8} chickens."
print(txt.format(49))完整实例3：
#To demonstrate, we insert the number 8 to specify the available space for the value.
#Use "=" to place the plus/minus sign at the left most position:
txt = "The temperature is {:=8} degrees celsius."
print(txt.format(-5))完整实例4：
#Use "+" to always indicate if the number is positive or negative:
txt = "The temperature is between {:+} and {:+} degrees celsius."
print(txt.format(-3, 7))完整实例5：
#Use "-" to always indicate if the number is negative (positive numbers are displayed without any sign):
txt = "The temperature is between {:-} and {:-} degrees celsius."
print(txt.format(-3, 7))完整实例6：
#Use " " (a space) to insert a space before positive numbers and a minus sign before negative numbers:
txt = "The temperature is between {: } and {: } degrees celsius."
print(txt.format(-3, 7))完整实例7：
#Use "," to add a comma as a thousand separator:
txt = "The universe is {:,} years old."
print(txt.format(13800000000))完整实例8：
#Use "_" to add a underscore character as a thousand separator:
txt = "The universe is {:_} years old."
print(txt.format(13800000000))完整实例9：
#Use "b" to convert the number into binary format:
txt = "The binary version of {0} is {0:b}"
print(txt.format(5))完整实例10：
#Use "d" to convert a number, in this case a binary number, into decimal number format:
txt = "We have {:d} chickens."
print(txt.format(0b101))完整实例11：
#Use "e" to convert a number into scientific number format (with a lower-case e):
txt = "We have {:e} chickens."
print(txt.format(5))完整实例12：
#Use "E" to convert a number into scientific number format (with an upper-case E):
txt = "We have {:E} chickens."
print(txt.format(5))完整实例13：
#Use "f" to convert a number into a fixed point number, default with 6 decimals, but use a period followed by a number to specify the number of decimals:
txt = "The price is {:.2f} dollars."
print(txt.format(45))
#without the ".2" inside the placeholder, this number will be displayed like this:
txt = "The price is {:f} dollars."
print(txt.format(45))完整实例14：
#Use "F" to convert a number into a fixed point number, but display inf and nan as INF and NAN:
x = float('inf')
txt = "The price is {:F} dollars."
print(txt.format(x))
#same example, but with a lower case f:
txt = "The price is {:f} dollars."
print(txt.format(x))完整实例15：
#Use "o" to convert the number into octal format:
txt = "The octal version of {0} is {0:o}"
print(txt.format(10))完整实例16：
#Use "x" to convert the number into Hex format:
txt = "The Hexadecimal version of {0} is {0:x}"
print(txt.format(255))完整实例17：
#Use "X" to convert the number into upper-case Hex format:
txt = "The Hexadecimal version of {0} is {0:X}"
print(txt.format(255))完整实例18：
#Use "%" to convert the number into a percentage format:
txt = "You scored {:%}"
print(txt.format(0.25))
#Or, without any decimals:
txt = "You scored {:.0%}"
print(txt.format(0.25))