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法律研究如何在 Python 中将数据值插入字符串？
我们可以使用各种格式将数据值插入字符串。我们可以用它来调试代码、生成报表、表单和其他输出。在本主题中，我们将了解三种字符串格式化方法以及如何将数据值插入字符串。
Python 有三种格式化字符串的方法
% - 旧式方法（Python 2 和 3 中都支持）
() - 新式方法（Python 2.6 及以上版本）
{} - f-字符串（Python 3.6 及以上版本）
旧式方法：%
旧式字符串格式化的形式为 format_string % data。格式字符串不过是插值序列。
| 语法 | 描述 |
|---|---|
| %s | 字符串 |
| %d | 十进制 |
| %x | 十六进制整数 |
| %o | 八进制整数 |
| %f | 十进制浮点数 |
| %e | 指数浮点数 |
| %g | 十进制或指数浮点数 |
| %% | 字面量 % |
# printing integer with % style type.
print('output \nprinting a number in string format %s' % 42)
print('printing a number in string decimal %d' % 42)
print('printing a number in string hexa-int %x' % 42)
print('printing a number in string exponential-float %g' % 42)输出
printing a number in string format 42 printing a number in string decimal 42 printing a number in string hexa-int 2a printing a number in string exponential-float 42
使用旧格式 % 进行字符串和整数插值
字符串中的 %s 表示插入一个字符串。字符串中 % 出现的次数需要与 % 后面字符串之后的的数据项数量相匹配。
单个数据项紧随其后的那个最终 %。多个数据必须分组到一个元组中，请参见下面的示例。
您还可以将格式字符串中 % 和类型说明符之间的其他值添加到指定最小和最大宽度、对齐方式以及填充字符。
1. + means right-align 2. - means left-align 3. . means separate minwidth and maxchars. 4. minwidth means mimimu field width to use 5. maxchars means how many characters/digits to print from the data value
player = 'Roger Federer'
country = 'Legend'
titles = 20
# note please try this only on Python 2. If you are running on Python3 output for below commands will vary a lot.
print('Output \n*** Tennis player %s From %s had won %d titles ' %(player,country,titles))
print('%s' % player) # print player
print('%5s' % player) # print firstname of player
print('%-7s' % player) # Last Name of player
print('%5.7s' % player) # Last Name of player with 5 leading spaces输出
*** Tennis player Roger Federer From Legend had won 20 titles Roger Federer Roger Federer Roger Federer Roger F
使用新式方法：{} 进行字符串和整数插值
如果您使用的是 Python 3.5 或更高版本，则可以使用下面部分中描述的“新式”格式化。
“{}” 格式化的语法为 format_string.format(data)。
请记住，format() 函数的参数需要按照格式字符串中 {} 占位符的顺序排列。有时为了提高可读性，您可以将字典或命名参数传递给 format。
player = 'Roger Federer'
player = 'Roger_Federer'
country = 'Legend'
titles = 20
print('Output \n{}'.format(player))
print(' *** Tennis player {} From {} had won {} titles '.format(player,country,titles))
# positonal arguments
print(' *** Tennis player {1} From {2} had won {0} titles '.format(titles,player,country))
# named arguments
print(' *** Tennis player {player} From {country} had won {titles} titles '.format(player = 'Roger Federer',country = 'Legend',titles = 20))
# Dictionary arguments
print(' *** Tennis player {player} From {country} had won {titles} titles '.format(player = 'Roger Federer',country = 'Legend',titles = 20))
# alignment left '<' (default)
print(' *** Tennis player {} From {:<5s} had won {:<5d} titles '.format(player,country,titles))
# alignment left '<' (default)
print(' *** Tennis player {} From {:<5s} had won {:<5d} titles '.format(player,country,titles))
# alignment center '^'
print(' *** Tennis player {} From {:^10s} had won {:^10d} titles '.format(player,country,titles))
# alignment right '>'
print(' *** Tennis player {} From {:>10s} had won {:>10d} titles '.format(player,country,titles))输出
Roger_Federer *** Tennis player Roger_Federer From Legend had won 20 titles *** Tennis player Roger_Federer From Legend had won 20 titles *** Tennis player Roger Federer From Legend had won 20 titles *** Tennis player Roger Federer From Legend had won 20 titles *** Tennis player Roger_Federer From Legend had won 20 titles *** Tennis player Roger_Federer From Legend had won 20 titles *** Tennis player Roger_Federer From Legend had won 20 titles *** Tennis player Roger_Federer From Legend had won 20 titles
使用最新式方法：f-字符串 进行字符串和整数插值
f-字符串出现在 Python 3.6 中，并很快成为推荐的字符串格式化方式。我个人使用这种格式。要创建 f-字符串
1. 在起始/初始引号之前使用字母 f/F。
2. 在花括号 ({}) 内包含变量名或表达式以将其值插入字符串。
player = 'Roger_Federer'
country = 'Legend'
titles = 20
print(f"Output \n *** Tennis player {player} From {country} had won {titles} titles ")
print(f" *** I hope {player} wins another {titles - 10} titles ")
print(f" {'*' * 3} Tennis player {player.upper()} From {country:.^10} had won {titles} titles")输出
*** Tennis player Roger_Federer From Legend had won 20 titles *** I hope Roger_Federer wins another 10 titles *** Tennis player ROGER_FEDERER From ..Legend.. had won 20 titles
现在我们已经介绍了基础知识，让我们进入一些实际问题，以及我为什么建议开始使用格式化字符串。
titles = [
('federer', 20),
('nadal', 20),
('djokovic', 17),
]
print('Output\n')
for i, (player, titles) in enumerate(titles):
print('#%d: %-10s = %d' % (
i + 1,
player.title(),
round(titles)))输出
#0: federer = 20 #1: nadal = 20 #2: djokovic = 17
显然，在向高层发送报告时，不希望看到从 0 开始的索引，他们希望从 1 开始。罗杰·费德勒作为网球传奇人物，我个人希望将他表示为 #1 而不是 #0。
现在要进行更改，请查看在使用旧格式时代码的可读性是如何变化的。
titles = [
('federer', 20),
('nadal', 20),
('djokovic', 17),
]
print('Output\n')
for i, (player, titles) in enumerate(titles):
print('#%d: %-10s = %d' % (
i + 1,
player.title(),
round(titles)))输出
#1: Federer = 20 #2: Nadal = 20 #3: Djokovic = 17
总之，我提供了一个示例来说明为什么 f-字符串更容易管理。
old_school_formatting = (
' Tennis Legeng is %(player)s, '
' %(player)s had won %(titles)s titles, '
'and he is from the country %(country)s.')
old_formatted = old_school_formatting % {
'player': 'Roger Federer',
'titles': 20,
'country': 'Swiss',
}
print('Output\n' + old_formatted)输出
Tennis Legeng is Roger Federer, Roger Federer had won 20 titles, and he is from the country Swiss.
new_formatting = (
' Tennis Legeng is {player}, '
' {player} had won {titles} titles, '
'and he is from the country {country}')
new_formatted = new_formatting.format(
player= 'Roger Federer',
titles= 20,
country= 'Swiss',
)
print('Output\n' + new_formatted)输出
Tennis Legeng is Roger Federer, Roger Federer had won 20 titles, and he is from the country Swiss
这种风格稍微不太冗余，因为它消除了字典中的一些引号以及格式说明符中相当多的字符，但它并不引人注目。
更新于： 2020-11-10
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