Preface
Python has added a new string formatting method in version 2.6: str.format(). Its basic syntax is to replace the previous %. with {} and :.
Placeholder syntax when formatting:
replacement_field ::= "{" [field_name] ["!" conversion] [":" format_spec] "}"Copy after login
"Mapping" rules
By position
str.format() Can accept unlimited parameters, and the positions can be out of order:
>>> "{0} {1}".format("hello", "world")
'hello world'
>>> "{} {}".format("hello", "world")
'hello world'
>>> "{1} {0} {1}".format("hello", "world")
'world hello world'Copy after login
By keyword parameters
When using key parameters, the parameter name needs to be provided in the string:
>>> "I am {name}, age is {age}".format(name="huoty", age=18)
'I am huoty, age is 18'
>>> user = {"name": "huoty", "age": 18}
>>> "I am {name}, age is {age}".format(**user)
'I am huoty, age is 18'Copy after login
Through object properties
str.format() User properties can be read directly:
>>> class User(object):
... def __init__(self, name, age):
... self.name = name
... self.age = age
...
... def __str__(self):
... return "{self.name}({self.age})".format(self=self)
...
... def __repr__(self):
... return self.__str__()
...
...
>>> user = User("huoty", 18)
>>> user
huoty(18)
>>> "I am {user.name}, age is {user.age}".format(user=user)
'I am huoty, age is 18'Copy after login
By subscript
Elements can be accessed by subscripts inside the string that needs to be formatted:
>>> names, ages = ["huoty", "esenich", "anan"], [18, 16, 8]
>>> "I am {0[0]}, age is {1[2]}".format(names, ages)
'I am huoty, age is 8'
>>> users = {"names": ["huoty", "esenich", "anan"], "ages": [18, 16, 8]}
>>> "I am {names[0]}, age is {ages[0]}".format(**users)Copy after login
Specify conversion
You can specify the conversion type of string:
conversion ::= "r" | "s" | "a"
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Where "!r" corresponds to repr(); "!s" corresponds to str(); "!a" corresponds to ascii(). Example:
>>> "repr() shows quotes: {!r}; str() doesn't: {!s}".format('test1', 'test2')
"repr() shows quotes: 'test1'; str() doesn't: test2"Copy after login
Format Qualifier
Padding and Alignment
Padding is often used together with alignment. ^, <, > are respectively centered, left-aligned, and right-aligned, followed by width, and the character followed by : can only be one character. If not specified, it will be filled with spaces by default.
>>> "{:>8}".format("181716")
' 181716'
>>> "{:0>8}".format("181716")
'00181716'
>>> "{:->8}".format("181716")
'--181716'
>>> "{:-<8}".format("181716")
'181716--'
>>> "{:-^8}".format("181716")
'-181716-'
>>> "{:-<25}>".format("Here ")
'Here -------------------->'Copy after login
Floating point precision
Use f to represent the floating point type, and you can add precision control in front of it ：
>>> "[ {:.2f} ]".format(321.33345)
'[ 321.33 ]'
>>> "[ {:.1f} ]".format(321.33345)
'[ 321.3 ]'
>>> "[ {:.4f} ]".format(321.33345)
'[ 321.3335 ]'
>>> "[ {:.4f} ]".format(321)
'[ 321.0000 ]'Copy after login
You can also specify a symbol for floating point numbers, + means + will be displayed before positive numbers, and - will be displayed before negative numbers; (space) means before positive numbers Adding a space and adding -;- before a negative number is consistent with adding nothing ({:f}):
>>> '{:+f}; {:+f}'.format(3.141592657, -3.141592657)
'+3.141593; -3.141593'
>>> '{: f}; {: f}'.format(3.141592657, -3.141592657)
' 3.141593; -3.141593'
>>> '{:f}; {:f}'.format(3.141592657, -3.141592657)
'3.141593; -3.141593'
>>> '{:-f}; {:-f}'.format(3.141592657, -3.141592657)
'3.141593; -3.141593'
>>> '{:+.4f}; {:+.4f}'.format(3.141592657, -3.141592657)
'+3.1416; -3.1416'Copy after login
Specify the base system
>>> "int: {0:d}; hex: {0:x}; oct: {0:o}; bin: {0:b}".format(18)
'int: 18; hex: 12; oct: 22; bin: 10010'
>>> "int: {0:d}; hex: {0:#x}; oct: {0:#o}; bin: {0:#b}".format(18)
'int: 18; hex: 0x12; oct: 0o22; bin: 0b10010'Copy after login
Thousand separator
You can use "," as the thousands separator:
>>> '{:,}'.format(1234567890)
'1,234,567,890'Copy after login
Percent display
>>> "progress: {:.2%}".format(19.88/22)
'progress: 90.36%'Copy after login
In fact, format Also supports more type symbols:
type ::= "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "s" | "x" | "X" | "%"
Copy after login
Other tips
Placeholder nesting
Sometimes placeholder nesting is still useful:
>>> '{0:{fill}{align}16}'.format("hello", fill='*', align='^')
'*****hello******'
>>>
>>> for num in range(5,12):
... for base in "dXob":
... print("{0:{width}{base}}".format(num, base=base, width=5), end=' ')
... print()
...
...
5 5 5 101
6 6 6 110
7 7 7 111
8 8 10 1000
9 9 11 1001
10 A 12 1010
11 B 13 1011Copy after login
As When using the function
, you can not specify the format parameters first, but call it as a function in an unnecessary place:
>>> email_f = "Your email address was {email}".format
>>> print(email_f(email="suodhuoty@gmail.com"))
Your email address was sudohuoty@gmail.comCopy after login
Escape braces
When you need to use braces in a string, you can use braces to escape:
>>> " The {} set is often represented as { {0} } ".format("empty")
' The empty set is often represented as {0} 'Copy after login
For more detailed introduction to string formatting str.format in Python and related articles, please pay attention to the PHP Chinese website!
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