(Basic Python tutorial) learning notes | chapter 03rd | string

(Basic Python tutorial) learning notes | chapter 03rd | string

Chapter 2: Using strings

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Supported operations

Index slices add elements to delete elements update element search elements (check whether an element is a member of a sequence) sequence length maximum value minimum other built-in functions

>>> Website = 'HTTP: // www.python.org '>>> website [-3:] = 'com' # this operation is invalid because the string remains unchanged, traceback (most recent call last) cannot be modified: File"
  
   
", Line 1, in
   
    
Website [-3:] = 'com' TypeError: 'str' object does not support item assignment
   
  

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String formatting:
% S: conversion specifier ancestor


# Stable type> str1 = "Hello, % s. % s enough for you ya? ">>> Val1 = ('Jerry ', 'hot') >>> print str1 % val1Hello, Jerry. Hot enough for you ya? # Floating point type> format = "PI with three decimals: %. 3f ">>> from math import pi >>> print format % piPI with three decimals: 3.142 Note: 1. if a list is used, the sequence is understood as a value. Only the ancestor and dictionary can format more than one value. percent: % Template string # similar to replacing variables in linux, Template, substitute (convert passed parameters) >>> s = Template ('$ x, glorious $ x! ') >>> S. substitute (x = 'slurm')' slurm, glorous slurm! '# If it is part of a word, enclose it with {}> s = Template (' I love $ {x} rry! ') >>> S. substitute (x = 'she')' I love Sherry! '# If it is a dollar, pay attention to the $ symbol, safe_substitute does not report errors due to missing values or dollar signs >>> s = Template ('using $ buy $ {x }! ') >>> S. substitute (x = 'food')' Using $ buy food! '# Use the dictionary to provide key/value pairs >>> s = Template ('A $ thing must never $ Action') >>> d = {}>>> d ['action'] = 'gentleman '>>> d ['action'] = 'show his socks' >>> s. substitute (d) 'A gentleman must never show his socks '>>> s = Template (' I am $ {name}, $ {age} years old. ') >>> d = {'name': 'Jerry', 'age': 50 }>>> s. substitute (d) 'I am Jerry, 50 years old. '#>>> s =' % s plus % s equals % s' % (, 2) >>> print s1 plus 1 equals 2

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Basic conversion specifiers:

(1) % characters, marking the start of conversion
(2) Conversion mark (optional)


-Left alignment + Positive and negative signs before conversion value "" blank character, indicating that the space 0 is reserved before the positive number is not enough, then 0 is used to fill (3) the minimum field width (optional):
Min width with specified value. If it is *, the value is read from the ancestor (4). accuracy value (optional)
If it is a real number, the precision value indicates the number of digits after it is a character, the precision value indicates the maximum width after it is *, and the precision value reads (5) the conversion type from the ancestor.





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Simple Conversion


>>> print 'price of eggs is %d' % 12price of eggs is 12>>> print 'Hexadecimal price of eggs: %x' % 42Hexadecimal price of eggs: 2a>>> from math import pi>>> 'Pi: %f...' % piPi: 3.141593...>>> 'very inexact estimate of pi: %i' % pivery inexact estimate of pi: 3>>> 'Using str: %s' % 42LUsing str: 42>>> 'Using repr: %r' % 42LUsing repr: 42L

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Field width and precision
Both parameters are integers separated by.. If only the precision is given, it must contain a vertex number.


>>> '% 10f' % pi # The width is 10' 3.141593' >>>' % 10.2f '% pi # The width is 10, the precision is 2 '000000'> '%. 2f '% pi # The precision is 2' 3. 14'> '%. 5s '%' Hello, world! '# String Length 'hello' >>>' %. * s' % (5, 'Hello, World! ') # String Length, whose value reads 'hello' from the ancestor'

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