Some useful python syntax encounter

A string

1.1 split a string:

s = "123*456*789*"
split_all = s.split("*")  # ['123', '456', '789', '']
split_1 = s.split("*",1)  # ['123', '456*789*']

1.2 character replacement

s = "123*456*789*"
s = s.replace("*","")  # 123456789

1.3 substring count

This sub-string can be a single character, it can be a string

# str.count(sub, start= 0,end=len(string))
str = "123*456*789"
num = str.count("123")  # 1
num = str.count("*")    # 2

1.4 Regularization

Regularization need to use this package re

import re
s = "123*456*789"
s_split = re.split("\*", s)  # ['123', '456', '789']  \*是正则语句

Two, list

2.1 Index

Multidimensional list element index, unlike np.array can write array [i, j] directly, but to write list [i] [j]

Delete the specified items 2.2

list = [1,2,1,1,3,4]
list.remove(1)         # [2, 1, 1, 3, 4]

Adding 2.3 list

adding the list corresponds to append

a = [1,2]
a = a + [1]   # [1,2,1] 相当于 a.append(1)  

2.4, list of copy:

Do not use list.copy () This is a shallow copy, for multi-layer list is invalid. Use a copy of this package

import copy
list = [[1],[2]]
list2 = copy.deepcopy(list)

2.5 list sorting

the list.sort () only for the object list. For other iteration object, use the sorted () function. sorted Function Reference https://www.runoob.com/python/python-func-sorted.html

# list.sort(cmp=None, key=None, reverse=False)  默认从小到大排序
list = [4,6,2,7,8,1]
list.sort()  # [1, 2, 4, 6, 7, 8]

# 方法二，可对所有可迭代的数排序
# sorted(iterable, cmp=None, key=None, reverse=False)
list2 = sorted(list)

Three, dictionary

3.1 ordinary dictionary:

dic = {}
dic["a"] = 1  # {'a':1}

3.2 collections package

This package contains a number of special dictionaries, reference:  https://www.jianshu.com/p/f2a429aa5963

Which has a value with a default dictionary defaultdict. On an ordinary dictionary, a call there have been no key will complain, but collection.defaultdict, this key will assign a default value.

import collections
dic = collections.defaultdict(lambda:1)  # 默认初始值是 1
dic = collections.defaultdict(lambda:[]) # 默认初始值为一个空的list

Dictionary 3.3 Other properties

Reference: https://www.runoob.com/python/python-dictionary.html 

No.	Functions and Description
1	dict.clear () All elements in the deleted dictionary
2	dict.copy () Returns a shallow copy of the dictionary
3	dict.fromkeys (seq [, val]) creates a new dictionary, the sequence elements do seq dictionary key, val a dictionary initial value corresponding to all keys
4	dict.get (key, default = None) Returns the specified key, if the return value is not in the dictionary default value
5	dict.has_key (key) if the key is in the dictionary dict returns true, otherwise returns false
6	dict.items () to return may traverse the list (key, value) tuples array
7	dict.keys () to return a list of all the keys dictionary
8	dict.setdefault (key, default = None) and get () is similar, but if the key does not exist in the dictionary, and will add value to default keys
9	dict.update (dict2) to dict2 dictionary of key / value pairs in the update to the dict
10	dict.values () all values in the list returned dictionary
11	pop (key [, default]) value of a given key to delete the dictionary corresponding to the key, the return value is deleted. key value must be given. Otherwise, return default values.
12	popitem () to go back and delete the last pair of keys and values in the dictionary.

 Fourth, digital

it (whether)	Absolute value
num1 // num2	Divisible
num1 % num2	Take the remainder
num1 ** num2	Index num1 ^ num2