Python Learning Note 8: Basics (String formatting)

Reference: http://www.cnblogs.com/wupeiqi/articles/5484747.html

There are two ways to format a Python string: a percent-semicolon, format-mode

The percent of the semicolon is relatively old, and format is a more advanced way to replace the old way, the two coexist. [PEP-3101]

This PEP proposes a new system for built-in string formatting operations, intended as a replacement for the existing '% ' s Tring formatting operator.

1, percent of the way

%[(name)][flags][width]. [Precision]typecode

• (name) optional, used to select the specified key
• Flags are optional, and the values to choose from are:
  • + Right-aligned, positive plus, negative before plus minus;
  • -left-justified; no sign before positive number, plus minus sign before negative number;
  • Spaces are right-justified, plus a positive number before a negative number plus a minus sign;
  • 0 Right alignment, no sign before positive number, minus sign before negative, and 0 padding in blank
• Width selectable, occupied widths
• . Precision optional, number of digits retained after the decimal point
• TypeCode must choose
  
  • S, gets the return value of the __str__ method of the passed-in object and formats it to the specified location
  • R, gets the return value of the __repr__ method of the passed-in object and formats it to the specified location
  • C, Integer: Converts a number to its Unicode corresponding value, 10 binary range is 0 <= i <= 1114111 (py27 only supports 0-255); character: add character to specified position
  • O, converts an integer to an octal representation and formats it to a specified location
  • X, converts an integer to a hexadecimal representation and formats it to a specified location
  • D, converts an integer, floating-point number to a decimal representation, and formats it to a specified position
  • E, converting integers, floating-point numbers to scientific notation, and formatting them to a specified location (lowercase e)
  • E, converting integers, floating-point numbers into scientific notation, and formatting them to a specified position (uppercase E)
  • F, converts an integer, floating-point number to a floating-point number representation, and formats it to a specified position (the default is 6 digits after the decimal point)
  • F, ibid.
  • G, auto-adjust convert integers, floating-point numbers to floating-point or scientific notation (more than 6 digits in scientific notation), and format them to a specified location (if scientific counts are e;)
  • G, auto-adjust convert integers, floating-point numbers to floating-point or scientific notation (more than 6 digits in scientific notation), and format them to a specified location (if scientific counts are e;)
  • %, when there is a format flag in the string, a percent sign is required

Note: There is no way to automatically convert an integer to a binary representation in Python with a percent-semicolon format

Common formatting:

1234567891011

tpl ="i am %s"%"alex"tpl ="i am %s age %d"%("alex", 18)tpl ="i am %(name)s age %(age)d"%{"name": "alex", "age": 18}tpl ="percent %.2f"% 99.97623tpl ="i am %(pp).2f"%{"pp": 123.425556, }tpl ="i am %.2f %%"%{"pp": 123.425556, }

2. Format mode

[[Fill]align] [Sign] [#] [0] [Width] [,] [. Precision] [Type]

• Fill "optional" white space filled with characters
• Align "optional" alignment (required with width)
• <, content left justified
• Content right-aligned (default)
• =, the content is right-aligned, the symbol is placed to the left of the padding character, and only valid for numeric types. Even: symbol + filler + number
• ^, content centered
• Sign "optional" with unsigned numbers
  • +, positive home Plus, minus plus negative;
  • -The plus sign does not change, minus is negative;
  • Spaces, plus spaces, minus signs and negative;
• # "optional" for binary, octal, hex, if added #, 0b/0o/0x is displayed, otherwise not displayed
• , "optional" adds a delimiter to the number, such as: 1,000,000
• width "Optional" format the size of the placeholder
• . Precision "optional" decimal digits reserved Precision
• Type "optional" formatting types
  • Parameters passed into the string type
    • s, format string type data
    • Blank, no type specified, default is None, same as S
  • Parameters passed into the integer type
    
    • B, automatic conversion of 10 binary integers to 2 binary representation and then formatting
    • C, automatic conversion of 10 binary integers to their corresponding Unicode characters
    • d, decimal integer
    • O, the 10 binary integers are automatically converted to 8 binary representation and then formatted;
    • X, automatically converts 10 binary integers to 16 binary representation and then formats (lowercase x)
    • X, automatically converts 10 binary integers to 16 binary representation and then formats (uppercase X)
  • Parameters passed in floating-point or decimal type
    • E, converted to scientific notation (lowercase e), and then formatted;
    • E, converted to scientific notation (capital E), and then formatted;
    • F, converted to floating-point type (6 digits after the default decimal point), and then formatted;
    • F, converted to floating-point type (6 digits after the default decimal point), and then formatted;
    • G, automatically switch between E and F
    • G, automatically switch between E and F
    • %, display percent (default 6 digits after decimal)

Common formatting:

1234567891011121314151617181920212223242526272829

tpl ="i am {}, age {}, {}".format("seven", 18, ‘alex‘) tpl = "i am {}, age {}, {}".format(*["seven", 18, ‘alex‘]) tpl ="i am {0}, age {1}, really {0}".format("seven", 18) tpl ="i am {0}, age {1}, really {0}".format(*["seven", 18]) tpl ="i am {name}, age {age}, really {name}".format(name="seven", age=18) tpl ="i am {name}, age {age}, really {name}".format(**{"name": "seven", "age": 18})  tpl ="i am {0[0]}, age {0[1]}, really {0[2]}".format([1, 2, 3], [11, 22, 33]) tpl ="i am {:s}, age {:d}, money {:f}".format("seven", 18, 88888.1) tpl = "i am {:s}, age {:d}".format(*["seven", 18]) tpl ="i am {name:s}, age {age:d}".format(name="seven", age=18) tpl ="i am {name:s}, age {age:d}".format(**{"name": "seven", "age": 18})tpl ="numbers: {:b},{:o},{:d},{:x},{:X}, {:%}".format(15, 15, 15, 15, 15, 15.87623, 2)tpl ="numbers: {:b},{:o},{:d},{:x},{:X}, {:%}".format(15, 15, 15, 15, 15, 15.87623, 2)tpl ="numbers: {0:b},{0:o},{0:d},{0:x},{0:X}, {0:%}".format(15)tpl ="numbers: {num:b},{num:o},{num:d},{num:x},{num:X}, {num:%}".format(num=15)

More formatting operations: https://docs.python.org/3/library/string.html

Python Learning Note 8: Basics (String formatting)