Python Primer

Getting Started

• 파이썬

• 아나콘다

• VS Code

• Positron

print

Mutable and slice

Python Objects

• Each object has a list of attributes

• Any attribute attr of an object obj can be accessed via the dot notation

Types and Operators

• Each object has a type:
  • str, int, float, …

• reference

• Operator overloading: Operators such as + and * can be defined for other data types as well

Functions and Methods

• Compute population mean and variance

Modules

• 모듈: 관련 함수, 클래스, 변수 등을 그룹화한 파일(.py 파일)
  • datetime, matplotlib, numpy, os, pandas, …

Flow Control

• while, for, if-else, …

Iteration

Sets

• Python sets are unordered collections of unique objects {}

Lists

• 리스트: 중복(값은 값 여러 번 포함) 가능, 순서 보장 가능(요소들이 추가된 순서대로 저장됨, 인덱스로 접근할 수 없음), 수정 가능(요소의 추가, 삭제, 변경 가능)

• Set: 중복된 값을 허용하지 않고, 순서를 보장하지 않고(따라서 인덱스로 접근할 수 없음), 요소의 추가 및 삭제가 가능하나 특정 위치의 요소를 변경하는 것은 불가능

Dictonary

• 딕셔너리: key:value의 조합으로 이루어짐, 키를 사용하여 값에 접근, 키는 중복될 수 없지만 값은 중복될 수 있음

Classes

• 새로운 클래스 만드는 예시

Files

• 교재에 있는 예제 직접 해 보세요

Numpy

• Numpy의 삼각함수

Creating and shaping arrays

• The fundamental data type in numpy is the ndarray.

• Note that arange is numpy’s version of range, with the di↵erence that arange returns an ndarray object.

• The dimension of an ndarray can be obtained via its shape method, which returns a tuple.

• Arrays can be reshaped via the reshape method. This does not change the current ndarray object.

• hstack and vstack: The arrays are joined horizontally and vertically, respectively.

Slicing

• Arrays can be sliced similarly to Python lists.

• If an array has several dimensions, a slice for each dimension needs to be specified.

• ndarrays are mutable

Array Operations

• Basic mathematical operators and functions act element-wise on ndarray objects.

• Since version 3.5 of Python, it is possible to multiply two ndarrays using the @ operator (which implements the np.matmul method). For matrices, this is similar to using the dot method. For higher-dimensional arrays the two methods behave differently.

• numpy allows arithmetic operations on arrays of different shapes (dimensions).

Random numbers

• numpy에는 random이라는 sub-modules 존재

Matplotlib

• 산점도 예제

Pandas

• pandas: DataFrame 클래스를 포함하여 데이터 구성과 분석에 필요한 다양한 툴 제공

Extracting Information

• The apply method allows one to apply general functions to columns or rows of a DataFrame.

• The loc method allows for accessing elements (or ranges) in a data frame.

• count: Counts number of non-NA cells.

• The groupby method of a DataFrame object is useful for summarizing and displaying the data in manipulated ways.

• mean: Column/row mean.

Scikit-learn

Partitioning the Data

• train_test_split 함수로 자료 분할 가능

Standardization

• MinMaxScaler, StandardScaler 활용 가능

References

• Data Science and Machine Learning