[英]What does %s mean in a python format string?
What does %s
mean in Python? %s
在 Python 中是什么意思? And what does the following bit of code do?下面的代码有什么作用?
For instance...例如...
if len(sys.argv) < 2:
sys.exit('Usage: %s database-name' % sys.argv[0])
if not os.path.exists(sys.argv[1]):
sys.exit('ERROR: Database %s was not found!' % sys.argv[1])
It is a string formatting syntax (which it borrows from C).它是一种字符串格式化语法(它是从 C 中借来的)。
Please see "PyFormat" :请参阅“PyFormat” :
Python supports formatting values into strings.
Python 支持将值格式化为字符串。 Although this can include very complicated expressions, the most basic usage is to insert values into a string with the
%s
placeholder.尽管这可能包括非常复杂的表达式,但最基本的用法是将值插入带有
%s
占位符的字符串中。
Edit: Here is a really simple example:编辑:这是一个非常简单的例子:
#Python2
name = raw_input("who are you? ")
print "hello %s" % (name,)
#Python3+
name = input("who are you? ")
print("hello %s" % (name,))
The %s
token allows me to insert (and potentially format) a string. %s
标记允许我插入(并可能格式化)一个字符串。 Notice that the %s
token is replaced by whatever I pass to the string after the %
symbol.请注意,
%s
标记被我在%
符号后传递给字符串的任何内容替换。 Notice also that I am using a tuple here as well (when you only have one string using a tuple is optional) to illustrate that multiple strings can be inserted and formatted in one statement.另请注意,我在这里也使用了元组(当您只有一个字符串时,使用元组是可选的)来说明可以在一个语句中插入和格式化多个字符串。
Andrew's answer is good.安德鲁的回答很好。
And just to help you out a bit more, here's how you use multiple formatting in one string只是为了帮助您更多,这里是您如何在一个字符串中使用多种格式
"Hello %s, my name is %s" % ('john', 'mike') # Hello john, my name is mike".
If you are using ints instead of string, use %d instead of %s.如果您使用整数而不是字符串,请使用 %d 而不是 %s。
"My name is %s and i'm %d" % ('john', 12) #My name is john and i'm 12
The format
method was introduced in Python 2.6. format
方法是在 Python 2.6 中引入的。 It is more capable and not much more difficult to use:它功能更强大,使用起来也不难:
>>> "Hello {}, my name is {}".format('john', 'mike')
'Hello john, my name is mike'.
>>> "{1}, {0}".format('world', 'Hello')
'Hello, world'
>>> "{greeting}, {}".format('world', greeting='Hello')
'Hello, world'
>>> '%s' % name
"{'s1': 'hello', 's2': 'sibal'}"
>>> '%s' %name['s1']
'hello'
%s
and %d
are Format Specifiers or placeholders for formatting strings/decimals/floats etc. %s
和%d
是用于格式化字符串/小数/浮点数等的格式说明符或占位符。
MOST common used Format specifier:最常用的格式说明符:
%s
: string %s
: 字符串
%d
: decimals %d
: 小数
%f
: float %f
: 浮动
Self explanatory code:自解释代码:
name = "Gandalf"
extendedName = "the Grey"
age = 84
IQ = 149.9
print('type(name):', type(name)) #type(name): <class 'str'>
print('type(age):', type(age)) #type(age): <class 'int'>
print('type(IQ):', type(IQ)) #type(IQ): <class 'float'>
print('%s %s\'s age is %d with incredible IQ of %f ' %(name, extendedName, age, IQ)) #Gandalf the Grey's age is 84 with incredible IQ of 149.900000
#Same output can be printed in following ways:
print ('{0} {1}\'s age is {2} with incredible IQ of {3} '.format(name, extendedName, age, IQ)) # with help of older method
print ('{} {}\'s age is {} with incredible IQ of {} '.format(name, extendedName, age, IQ)) # with help of older method
print("Multiplication of %d and %f is %f" %(age, IQ, age*IQ)) #Multiplication of 84 and 149.900000 is 12591.600000
#storing formattings in string
sub1 = "python string!"
sub2 = "an arg"
a = "i am a %s" % sub1
b = "i am a {0}".format(sub1)
c = "with %(kwarg)s!" % {'kwarg':sub2}
d = "with {kwarg}!".format(kwarg=sub2)
print(a) # "i am a python string!"
print(b) # "i am a python string!"
print(c) # "with an arg!"
print(d) # "with an arg!"
%s
indicates a conversion type of string when using python's string formatting capabilities. %s
表示使用python的字符串格式化功能时字符串的转换类型。 More specifically, %s
converts a specified value to a string using the str()
function.更具体地说,
%s
使用str()
函数将指定值转换为字符串。 Compare this with the %r
conversion type that uses the repr()
function for value conversion.将此与使用
repr()
函数进行值转换的%r
转换类型进行比较。
Take a look at the docs for string formatting .查看字符串格式的文档。
In answer to your second question: What does this code do?...回答你的第二个问题:这段代码有什么作用?...
This is fairly standard error-checking code for a Python script that accepts command-line arguments.这是接受命令行参数的 Python 脚本的相当标准的错误检查代码。
So the first if
statement translates to: if you haven't passed me an argument, I'm going to tell you how you should pass me an argument in the future, eg you'll see this on-screen:所以第一个
if
语句转换为:如果你还没有给我传递一个参数,我将告诉你你将来应该如何传递一个参数,例如你会在屏幕上看到这个:
Usage: myscript.py database-name
The next if
statement checks to see if the 'database-name' you passed to the script actually exists on the filesystem.下一个
if
语句检查您传递给脚本的“数据库名称”是否确实存在于文件系统中。 If not, you'll get a message like this:如果没有,您将收到如下消息:
ERROR: Database database-name was not found!
From the documentation :从文档:
argv[0] is the script name (it is operating system dependent whether this is a full pathname or not).
argv[0] 是脚本名称(它是否为完整路径名取决于操作系统)。 If the command was executed using the -c command line option to the interpreter, argv[0] is set to the string '-c'.
如果命令是使用解释器的 -c 命令行选项执行的,则 argv[0] 设置为字符串“-c”。 If no script name was passed to the Python interpreter, argv[0] is the empty string.
如果没有脚本名称传递给 Python 解释器,则 argv[0] 是空字符串。
Here is a good example in Python3.这是 Python3 中的一个很好的例子。
>>> a = input("What is your name?")
What is your name?Peter
>>> b = input("Where are you from?")
Where are you from?DE
>>> print("So you are %s of %s" % (a, b))
So you are Peter of DE
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