Tips of Anaconda installation
For Anaconda distribution, this (mirror)[https://mirrors.tuna.tsinghua.edu.cn/anaconda/archive/] could be faster than the official.
(numpy tutorial)[https://docs.scipy.org/doc/numpy-dev/user/quickstart.html]
matrix with Jupyter1
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9%matplotlib inline
import sympy as sympy
import numpy as np
import matplotlib.pyplot as plt
import seaborn as sbn
from scipy import *
A = np.array(([.8,.3],[.2,.7]))
A.dot(x1)
Language Basic
| Question | Answer |
|---|---|
| 01.Access the last element of a list | aList[-1] // it can be interpreted as aList[len(aList)-1] |
| 02.Remove an element from a list | previousLastOne = aList.pop() or del aList[-1] The first one can get the removed one. |
| 03.Is it accessible for a (loop) variable after the loop (e.g. for ele in elements:) | Sadly, it is (e.g. ele). How to get rid of it? (del ele, ugly workaround) |
| 04.How to turn a range object to a list | list(range(1,5)) // range() returns a range object (iterable) and passed to list() to become a list |
| 05.How to slice a list | aList[-3:] // obviously here : needs specific syntax support |
| 06.Find if an element exists in a list/string | element in aList or sub_string in aString // it returns a boolean, a syntax keyword |
| 07.How to check empty string/list | if aList: or if aString: // empty string/list is false in for and if |
| 08.Loop through a dictionary | for k, v in aDict.items() |
| 09.Provide a description to a function/class/module | Put """...""" (docstring) below a function/class or at the beginning of a module |
| 10.Flexible number of function parameters | def foo(p, *pa): // put *pa after positioned parameters |
| 11.Flexible number of named parameters | def foo(**user_info) // Note the call side doesn’t need to create a dictionary to use user_info (see source code) |
| 12.Import a function with another name from a module | from a_module import function_a as function_b |
| 13.Arrange function parameters in multiple lines | use two TAB to make parameters look different from function body (see source code) |
| 14.Call methods of super class | super().__init__(...) |
| 15.Open a file without closing it explicitly | with open('file_name') as file_object: |
| 16.Loop through file object line by line | for line in file_object: |
| 17.Exception handling | try-except-else-finally block. Use pass in except branch to fail silently. |
| 18.Is there concept of Option | No. None is same as null. |
| 19.Check if variable is None | a is None // is not is to check the opposite |
| 20.Unpack sequence | a,b,*_ = ("foo","bar",1,2) // _ => [1,2] |
| 21.Performance of list insert, pop and in | For non-last element, it’s O(n) while n is the size of the list |
| 22.For loop with index | for i,value in enumerate(seq): |
| 23.Convert a list of rows into a list of columns | zip(*seq) //see source code |
| 24.Objects can be put in dictionary as key | number, string, tuple (immutable) or anything else has fixed value of hash(obj) |
| 25.Nested for comprehension | [v2 for v1 in s1 if ... for v2 in v1 if ...] |
| 26.Variable scope | There are two scopes: local and global. class, function can create nested scope, but not if/for/while. |
| 27.Currying | from functools import partial and partial(foo, some_variable) |
| 28.Generator in for comprehension | (x for x in ... if ...) or use yield in generator function |
| 29.Anonymous function | lambda x: x[0] |
| 30.Generator from itertools | groupby, combinations, product, permutations, etc. |
| 31.Catch multiple errors | except (TypeError, ValueError): |
1 | // 11 |