Python string formatting method use of the Format function

Python supports format from 2.6, a new, easier-to-read string formatting method that changes from the original% mode to a new, more readable

1. The curly braces declare {}, the parameter reference declaration before the render, and the curly brackets can use numbers to denote the ordinal of the reference parameter, or the variable name to refer directly.
2. The variable name introduced from the format parameter,
3. Colon:
4. The number of character bits declaration,
5. Declaration of a blank auto-fill character
6. Statement of the thousand-digit point
7. Declaration of a variable type: string s, Number D, floating point F
8. Alignment direction Symbols < ^ >
9. Property accessors in parentheses ?
10. Use an exclamation point! followed by A, R, S, declares which mode to use, acsii mode, reference __repr__, or __str__
11. Add the Magic function __format__ (self, format), you can customize the different display according to the format of the string before format, such as: ' {: xxxx} ' at this time XXXX will be passed as a parameter in the __FORMAT__ function.

A comprehensive example shows:

1. Such as: Thousands of points, floating point numbers, padding characters, the combination of alignment use:

Enter: ' {: >18,.2f} '. Format (70305084.0) #: Colon + blank padding + right-aligned + fixed-width 18 + floating-point precision. The F-output: ' 70,305,084.00 '

2. Complex data formatting

Input: Data = [4, 8, +, +, +] ' {d[4]} {d[5]} '. Format (d=data) output: 23 42

3. Complex Data formatting:

Input: Class Plant (object):
Type = ' Tree '
kinds = [{' name ': ' Oak '}, {' name ': ' Maple '}]

' {P.type}: {P.kinds[0][name]} '. Format (p=plant ()) Output: Tree:oak Classification Example:

• The curly braces declare {}, the parameter reference declaration before the render, and the curly brackets can use numbers to denote the ordinal of the reference parameter, or the variable name to refer directly.

' {{} {} '. Format (' One ', ' ' One ', ' ') ' {1} ' {0} '. Format (' One ', ' both ') OutputOne Setup

data = {' first ': ' Hodor ', ' last ': ' hodor! '}

Old

'% (first) s% (last) s '% data

New

' {first} {last} '. Format (**data)

Outputhodor hodor!

• The variable name introduced from the format parameter,

• Colon:, character digit declaration, blank auto-fill declaration, thousand-bit declaration, variable type declaration: string s, Number D, floating-point number F, Alignment direction symbol < ^ >

' {:. 5} '. Format (' xylophone ')

Outputxylop

' {: ^10} '. Format (' Test ')

Output Test

‘{:. {}} '. Format (' xylophone ', 7)

Outputxylopho

' {: 4d} '. Format (42)

Output 42

' {: 06.2f} '. Format (3.141592653589793)

Output003.14

' {: +d} '. Format (42)

OUTPUT+42: Enter: ' {: >18,.2f} ' using a combination of thousands of decimal points, floating-point numbers, padding characters, and alignment. Format (70305084.0) #: Colon + blank padding + right-aligned + fixed-width 18 + floating-point precision. The F-Output: ' 70, 305,084.00 '

• Property accessors in parentheses ?

Setup

person = {' first ': ' Jean-luc ', ' last ': ' Picard '}

New

' {P[first]} {P[last]} '. Format (P=person)

Output

Setup

data = [4, 8, 15, 16, 23, 42]

New

' {D[4]} {d[5]} '. Format (d=data)

Output23 Setup

Class Plant (object):    type = ' tree '    kinds = [{' name ': ' Oak '}, {' name ': ' Maple '}]

New

' {P.type}: {P.kinds[0][name]} '. Format (P=plant ())

Outputtree:oak

• Exclamation! Restrict access to magic functions such as __repr__:

Setup

Class Data (object):    def __str__ (self):        return ' str '    def __repr__ (self):        return ' repr '

Old

'%s%r '% (data (), data ())

New

' {0!s} {0!r} '. Format (Data ())

Outputstr repr

• Add the Magic function __format__ (self, format), you can customize the different display according to the format of the string before format, such as: ' {: xxxx} ' at this time XXXX will be passed as a parameter in the __FORMAT__ function.

Setup

Class HAL9000 (object):    def __format__ (self, format):        if (format = = ' Open-the-pod-bay-doors '):            return "I ' m Afraid I can ' t do that. "        Return ' HAL 9000 '

New

' {: open-the-pod-bay-doors} '. Format (HAL9000 ())

Outputi ' m afraid I can ' t do.

• Special cases of time and date:

Setup

From datetime import datetime

New

' {:%y-%m-%d%h:%m} '. Format (DateTime (2001, 2, 3, 4, 5))

output2001-02-03 04:05

Python string formatting method use of the Format function