Detailed explanation of Python string and dictionary related operations

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Python Detailed examples of string and dictionary related operations

String operations:

String % formatting operations:

str = "Hello,%s.%s enough for ya ?"
values = ('world','hot')
print str % values

Output result:

 Hello,world.hot enough for ya ?

Template string:

##

#coding=utf-8
from string import Template
## 单个变量替换
s1 = Template('$x, glorious $x!')
print s1.substitute(x = 'slurm')

## 美元符号表示以及单个变量的替换
s2 = Template("Make $$ selling $x!")
print s2.substitute(x = 'slurm')

## 字段变量的替换
s3 = Template('A $thing must never $action .')
d = {}
d['thing'] = 'gentleman'
d['action'] = 'show his socks'
print s3.substitute(d)

ps：safe_substitute 不会因缺少值或者不正确使用$字符而出错。

String formatting type:

(1) % character: marks the beginning of the conversion specifier, which is the beginning of replacement.

(2) - means left alignment, + means adding a plus or minus sign before converting the value. 0 means that if there are not enough digits in the conversion value, fill it with 0s.
(3) * The minimum field width can be specified.
(4) A dot (.) is followed by the precision value.

String methods:

(1) find: You can find a substring in a longer string and return the leftmost index of the location of the substring. If not found, it returns -1.

print 'With a moo-moo here, and a moo-moo there'.find('moo')
返回：7

(2) join method: Splice the strings together.

print '/'.join((' ','usr','bin','env'))
输出： /usr/bin/env
ps：和谷歌的guava有点像。

(3) lower method: Returns the lowercase version of the string.

print 'AK47'.lower()
输出：ak47

(4) replace method: Returns the string obtained after all matches of a certain string are replaced.

'This is a test'.replace（'is','ezz')
输出：Thezz ezz a test

(5) split method: the inverse method of join, which separates strings into sequences.

print '1+2+3+4+5'.split('+')
输出：['1', '2', '3', '4', '5']

(6) strip method: remove the strings on both sides. The default is a space string, you can also specify the corresponding string.

ps：另外可以参加lstrip和rstrip方法。

(7) translate method: Like the replace method, you can replace certain parts of the string, but unlike the former, the translate method only processes a single character. Its advantage is that it can perform multiple replacements at the same time, which is sometimes much more efficient than replace.

ps：maketrans方法和translate方法类似。

Basic operations of dictionary:

(1) dict method: used to construct dictionary data.

dict（name='Gumby',age=42)
dict([('name','Gumby'),('age',42)])
ps:都是构造字段的方法。

(2) Basic dictionary operations:

1. len(d) returns the number of items (key values) in d.

2. d[k] returns the value associated with key k.
3. d[k]=v associates value v to key k.
4. del d[k] deletes the item with key k.
5. k in d checks whether d contains an item with key k.

(3) The copy method returns a new dictionary with the same key-value pairs.

(4) fromkeys: method creates a new dictionary using the given keys, and the value corresponding to each key is None.

print {}.fromkeys(['name','age'])
输出：{'age': None, 'name': None}

(5) get method: The get method is a more relaxed dictionary item method.

d = {}
d['name'] 如此访问时会报错。
d.get('name')访问时，如果不存在会返回None。

(6) haskey: The haskey method can check whether the dictionary contains the given key. d.has_key(k) is equivalent to k in d.

(7) items and iteritems methods:

items方法会将字典按照键值元组列表的形式返回，但没有顺序。
iteritems和items类似，但是返回的是迭代器。

(8) keys and iterkeys are similar to items. This is a list or iterator that returns keys.

(9) The values ​​method returns the values ​​in the dictionary in list form. Unlike keys or iterkeys, the returned value can contain duplicate values.

(10) The update method can use one dictionary to update another dictionary.

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