add chapter 19 python code
fix wrong code path
add chapter 23 python code
Merge pull request #116 from zhouchang1988/master

add chapter 19 python code
Merge pull request #117 from zkld123/patch-1

fix wrong code path
add all chapter 01's python version code
Fixed layout problem
fix the code
Merge pull request #119 from jasonwbw/master

add all chapter 01's python version code
improve readability of chapter01.py
improve chapter19.py
improve chapter23.py
improve chapter21.py