& Lt; Basic Python tutorial & gt; learning notes | Chapter 1 | string, python Chapter 2

<Basic Python tutorial> learning notes | chapter 03rd | character string and python chapter 03rd

Chapter 2: Using strings

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Supported operations

• Index
• Slice
• Add Element
• Delete Element
• New Element
• Search for elements (check whether an element is a member of a sequence)
• Sequence length
• Maximum Value
• Minimum value
• 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 "<pyshell #162>", line 1, in <module> 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 the conversion value
• "" Blank character, indicating that space is reserved before a positive number
• If the value of 0 is not enough, fill it with 0.

(3) Minimum field width (optional ):

• Minimum width with a specified value
• If it is *, the value is read from the ancestor.

(4). Precision value (optional)

• If it is a real number, the precision value indicates the number of digits following it.
• If it is a character, the precision value indicates the maximum width
• If it is *, the precision value is read from the ancestor.

(5) Conversion Type

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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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Symbol, alignment, and 0 Filling

Before the field width and precision value, you can place a "standard table", which can be 0, +, "" >>>' % 010.2f '% pi # width is 10, accuracy 2, fill '100% with 0. 14' >>> 0108 >>>>' %-10.2f '% pi # Left alignment' 3. 14' # space. It is useful when the value is positive or negative> print ('% 5d' % 10) + '\ n' + (' % 5d '%-10) 10-10 # +, indicating whether it is a positive number or a negative number, marking its positive and negative value, useful in alignment> print ('% + 5d' % 10) + '\ n' + (' % + 5d '%-10) + 10-10

String format example

width = input('Enter number here:')price_width   = 10item_width    = width - price_widthheader_format   = '%-*s%*s'content_format  = '%-*s%*.2f'print '='*widthprint header_format  % (item_width,'Item',price_width,'Price')print '-'*widthprint content_format % (item_width,'Apples',price_width,0.4)print content_format % (item_width,'Pears',price_width,0.5)print content_format % (item_width,'Banana',price_width,8)print content_format % (item_width,'Tomato',price_width,6)print '='*width

Output result: Enter number here: 40 ============================================== = Item Price -------------------------------------- Apples 0.40 Pears 0.50 Banana 8.00 Tomato 6.00 ==================== ================

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String Method

Find: Search for characters in a long string, and return the leftmost index position. The first position is 0, and not found as-1.

# Find does not return a Boolean value:-1: 0 not found: Found, index is 0, that is, the start position >>> 'I love python '. find ('perl ')-1 >>>' I Love python '. find ('python') 7 >>> title = 'python is so funny language' # If the searched object is in the starting position, it is 0 >>> title. find ('python') 0 # If there are multiple, return the first matched index value >>> title. find ('O') 4 # This method can select the start point, end point> subject = '$ Get rich now !!! $ '# Search from 0 by default >>> subject. find ('$') 0 # Only the starting position is provided> subject. find ('$', 1) 20 # provides the start position and end point> subject. find ('!!! ', 0, 16)-1

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Join: Anti-split method, used to add elements to the queue

>>> Seq = [1, 2, 3, 4, 5] # Number list >>>> sep = '+' >>> sep. join (seq) Traceback (most recent call last): File "<pyshell #242>", line 1, in <module> sep. join (seq) TypeError: sequence item 0: expected string, int found >>> seq = ['1', '2', '3', '4 ', '5'] # string list >>> sep. join (seq) '1 + 2 + 3 + 4 + 5'> dirs = '', 'usr', 'bin ', 'env' # note the leading space >>> '/'. join (dirs) '/usr/bin/env'> print 'C: '+ '\\'. join (dirs) # Double backslash C: \ usr \ bin \ env

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Lower: Convert all strings to lowercase letters.

>>> 'Hello, world '. lower () 'Hello, world' # if the input is in uppercase, the value cannot be found >>> if 'Jerry 'in ['Jerry', 'Tom ', 'sherry', 'john']: print "Found it. "# in this case, convert it to lower case >>> if 'Jerry '. lower () in ['Jerry ', 'Tom', 'sherry', 'john']: print "Found it. "Found it.

# Title (): Upper letter >>> "This is a dog, that's a pig ". title () "This Is A Dog, That's A Pig" # capwords () in the string module can also enable the upper letter function >>> import string >>> string. capwords ('hello, world. ') 'Hello, world.'

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Replace: replace all after finding

>>> 'Tom and Jerry'.replace('Tom','Sherry')'Sherry and Jerry'

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Split: A very important method, the reverse method of join

>>> '1 + 2 + 3 + 4 + 5 '. split ('+') ['1', '2', '3', '4 ', '5'] >>> '/usr/bin/env/python '. split ('/') ['', 'usr', 'bin', 'env', 'python'] # If no Delimiter is provided, use a space, create a table and use line breaks to separate them >>> 'Using the default '. split () ['using', ''the, 'default']

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Strip: Removes the null characters on both sides of the string, excluding the character strings.

>>> 'How old are you? '. Strip ()' How old are you? '# If the input may contain spaces, use it with strip () >>> names = ['Jerry', 'sherry ', 'Tom '] >>> name = 'Jerry' >>> if name in names: print 'Find it. '>>> if name. strip () in names: print 'Find it. 'Find it.

# You can also specify the items to be removed. For example, if it is local, It is (remove the first micro-ends *!) >>> '*** Spam ** in * everyone !!! * ** ''' ** Spam * in * everyone !!! * ** '>' ** Spam * in * everyone !!! * ** '. Strip ('*! ') 'Spam * in * everyone'

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Translate: The same as replace, which can replace some parts of the string. Difference: translate only processes a single character.

Advantage: Multiple Replicas can be performed at the same time. Sometimes it is more efficient than replace. You need to prepare a conversion table before conversion.

>>> From string import maketrans # used in combination with maketrans >>> table = maketrans ('cs ', 'kz') # Use k to replace c, replace s with z> 'this is c character '. translate (table) 'thiz iz k kharakter'

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Functions in this Chapter

String. capwords (s [, sep]) use the split function to split the string and use capitalize to uppercase the first letter of each word;
The join function uses the sep as the separator to connect words.
String. maketrans (from, to) create a table for conversion

What is a string?

In vb
Dim str as string 'declares a string
Str = "231dd &" '231dd & is the content, and str is the variable name.
In C
Char s [] = {""}; // you can define an empty string as a variable s array.
S [1] = 'a'; // the first character is a. Note that single quotation marks are used here.
S [2] = '\ 0'; // string end

Character and string are different

Character is defined in the database
String is defined in programming languages.
For example, String str = 'Tom ';
In the database, the table has a field name that defines the character type, so str can be stored in this field of this table.