3.1.3 Syntax for formatting strings

Both the string Str.format () and the Formatter class Use the same formatted string. The formatted character uses curly braces {} to contain the replaced field, and any characters that are not in curly braces are directly output without conversion. Therefore, in order to output curly braces, you need to use a special way to output curly braces using double curly braces, such as { { to output {,}} to output }.

The syntax for formatting a string is as follows:

Replacement_field:: = "{" [Field_name] ["!" conversion] [":" Format_spec] "}"

Field_name:: = Arg_name ("." Attribute_name | "[" Element_index "]") *

Arg_name:: = [identifier | integer]

Attribute_name:: = Identifier

Element_index:: = Integer | Index_string

Index_string:: = <any source character except "]" > +

Conversion:: = "R" | "S" | A

Format_spec:: = <described in the next section>

3.1.3.1 format string Description strings

The syntax for the format string description strings is as follows:

Format_spec:: = [[Fill]align][sign][#][0][width][,][.precision][type]

Fill:: = <any character>

Align:: = "<" | ">" | "=" | "^"

Sign:: = "+" | "-" | " "

Width:: = integer

Precision:: = integer

Type:: = "B" | "C" | "D" | "E" | "E" | "F" | "F" | "G" | "G" | "N" | "O" | "S" | "X" | "X" | "%"

examples of 3.1.3.2 formatted strings

The following example uses the new format instead of using the old % format method. In most cases, however, the new format syntax is similar to the old syntax. Use curly braces {} and semicolons: Instead of percent sign %. For example , '%03.2f ' is represented as ' {: 03.2f} '. However, there are new options and different ways to use the new format, as in the following example:

To access parameters by location:

#string

Import string

Print (' {0},{1},{2} '. Format (' A ', ' B ', ' C ')

Print (' {},{},{} '. Format (' A ', ' B ', ' C ')

Print (' {2},{1},{0} '. Format (' A ', ' B ', ' C ')

Print (' {2},{1},{0} '. Format (* ' abc '))

Print (' {2},{1},{2} '. Format (' abc ', ' 123 ', ' 888 ')

The resulting output is as follows:

A,b,c

A,b,c

C,b,a

C,b,a

888,123,888

In this example, the statement ' {0},{1},{2} '. Format (' A ', ' B ', ' C ') in 0,1,2 is the ordinal of the positional parameter, {0} means toreplace the output with the parameter 'a' in this place, the ordinal of the positional parameter is from 0 starts counting, increasing from left to right.

In the statement' {},{},{} '. Format (' A ', ' B ', ' C '), if the position parameter is not specified, it is output by the default position, and if the number of curly braces is less than the number of positional arguments, then the output is ignored by the subsequent arguments. In the statement{2},{1},{0} '. Format (' A ', ' B ', ' C '), you can see that the position parameter can be placed in a different output position, so its output becomesCThe letters are output first, the last isaoutput. In the statement' {2},{1},{0} '. Format (* ' abc '), the parameter list parsing mechanism is used here, in the parameters 'ABC' before adding an asterisk*is to change the parameter to a list before processing, the position of each item in the list corresponds to the position parameter indicated at the output, so the output of this statement isC,b,athe order. In the statement' {2},{1},{2} '. Format (' abc ', ' 123 ', ' 888 '), the main point is that the positional parameters can be repeated or some positional parameters may be missing.

To access parameters by name:

Print (' Mouse: ({x},{y}) '. Format (x = ' + ', y = ' 200 ')

Mousept = {' x ': ' $ ', ' Y ': ' 888 '}

Print (' Mouse: ({x},{y}) '. Format (**mousept))

The resulting output is as follows:

Mouse: (100,200)

Mouse: (200,888)

In the statement ' mouse: ({x},{y}) '. Format (x = ' + ', y = ' $ ') , there is no number for the previous positional parameter, but instead of the name X, y . In the format parameter, of course, it is necessary to pass in the keyword parameter, in order to match these keyword parameters with the specified name of the output. In the statement ' mouse: ({x},{y}) '. Format (**mousept) , the dictionary parameter mousept is used directly to pass in, Then use two asterisks to parse the dictionary parameter back into the keyword parameter.

Properties for Access Parameters:

Print (' property access to complex number, real part ={0.real} imaginary part ={0.imag} '. Format (3 + 4j))

Class point:

def __init__ (self, x, y):

self.x, self.y = x, y

def __str__ (self):

Return ' point ({self.x}, {self.y}) '. Format (self = self)

Print (str (point (5,5)))

The output results are as follows:

Property access of complex number, real part =3.0 imaginary part =4.0

Point (5, 5)

In the statement ' Complex property access, real part ={0.real} imaginary part ={0.imag} '. Format (3 + 4j) , The properties of the complex are accessed directly in the format, and the resulting property can be output directly in the string. In the statement ' point ({self.x}, {self.y}) '. Format (self = self) , you can directly access the properties of the class, and the result prints the value of the Class property. This is much simpler than re-writing the attributes in the Format function, with fewer characters to enter.

Access the entry for the parameter:

XY = (20, 30)

Print (' X- axis : {0[0]}, Y - axis : {0[1]} '. Format (XY))

The output results are as follows:

X- Axis : Y- axis :

In this example, you can see that the item that accesses the tuple directly in the format, such as 0[0] , represents the first item that accesses the first parameter, and0[1] represents the second item that accesses the first parameter.

Replace %s and %r with !s and !r :

Print (' repr (): {!r}; str (): {!s} '. Format (' abc ', ' 123 '))

The output results are as follows:

Repr (): ' ABC '; STR (): 123

With this example, you can see the substitution of %swith!s, which issimpler and easier, and the same !r replaces the %r.

string arrangement and width alignment

Print (' {: <30} '. Format (' left justified '))

Print (' {: >30} '. Format (' right-justified '))

Print (' {: ^30} '. Format (' Center-aligned '))

Print (' {:* ^30} '. Format (' Center-aligned ')

The output results are as follows:

Align Left

Align Right

Center Alignment

Center Align *************

Replaces %+f,%-f , and % F, as well as floating-point number formatting for the specified symbol

Print (' {: +f}; {: +f} '. Format (0.618,-0.618))

Print (' {: F}; {: F} '. Format (0.618,-0.618))

Print (' {: F}; {: F} '. Format (0.618,-0.618))

Print (' {:-F}; {:-F} '. Format (0.618,-0.618)

The output results are as follows:

+0.618000; -0.618000

0.618000; -0.618000

0.618000; -0.618000

0.618000; -0.618000

Replace %x and %o, with the same value formatted as a different input output at the same time

Print (' int: {0:d}; Hex: {0:x}; Oct: {0:o}; Bin: {0:b} '. Format (55))

Print (' int: {0:d}; Hex: {1:x}; Oct: {0:o}; Bin: {0:b} '. Format (55, 64))

Print (' int: {0: #d}; Hex: {0: #x}; Oct: {0: #o}; Bin: {0: #b} '. Format (55))

The output results are as follows:

int:55; hex:37; oct:67; bin:110111

int:55; hex:40; oct:67; bin:110111

int:55; hex:0x37; oct:0o67; bin:0b110111

Use commas as separators for thousands

Print (' {:,} '. Format (9876543210))

Print (' {0:,} '. Format (88888888888889876543210))

The output results are as follows:

9,876,543,210

88,888,888,888,889,876,543,210

Output percent value when formatting

Print (' percent output:{:. 2%} '. Format (50/100))

Print (' percent output:{:. 2%} '. Format (1.08))

The output results are as follows:

Percent output:50.00%

Percent output:108.00%

Output time format when formatting

Import datetime

D = Datetime.datetime (2015, 1, 13, 12, 30, 59)

Print (' time format: {:%y-%m-%d%h:%m:%s} '. Format (d))

The output results are as follows:

Time format: 2015-01-13 12:30:59

Nested formatting parameters

For align, the text in Zip (' <^> ', [' left ' , ' Middle ', ' right '):

Print (' {0:{fill}{align}16} '. Format (text, fill=align, align=align))

width = 5

For NUM in range (5, 12):

For base in ' Dxob ':

Print (' {0:{width}{base}} '. Format (num, base=base, width=width), end = ')

Print ()

The output results are as follows:

Left <<<<<<<<<<<<<<<

^^ ^^ ^^ ^ ^^ ^^ ^^ ^^

>>>>>>>>>>>>>>> Right

5 5 5 101

6 6 6 110

7 7 7 111

8 8 10 1000

9 9 11 1001

Ten A 12 1010

B 13 1011

Multiple formatting templates and parallel

IPADDR = [192, 168, 0, 8]

Print (' {: 02x}{:02x}{:02x}{:02x} '. Format (*IPADDR))

The output results are as follows:

c0a80008

Cai Junsheng qq:9073204 Shenzhen

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3.1.3 Syntax for formatting strings