Python 3 学习笔记

Install Python From Source Code

You need use this method to install the latest Python if you cannot upgrade python via "apt-get, yum", for example, Friendly Arm".

A common problem like this:

#https://unix.stackexchange.com/questions/332641/how-to-install-python-3-6

I'd like to install the latest Python, which is 3.6 at the time of this post. However, the repository is saying that Python 3.4.2 is the newest version.

I've tried:

sudo apt-get update

sudo apt-get install python3

python3 is already the newest version.

python -V

Python 3.4.2

 

Some package need to be installed befor install Python to avoid some known problems

sudo apt-get install -y make build-essential libssl-dev zlib1g-dev   
sudo apt-get install -y libbz2-dev libreadline-dev libsqlite3-dev wget curl llvm 
sudo apt-get install -y libncurses5-dev  libncursesw5-dev xz-utils tk-dev

It is recommended to use make altinstall according to the official website.

Warning: make install can overwrite or masquerade the python binary. make altinstall is therefore recommended instead of make install since it only installs exec_prefix/bin/pythonversion.

wget https://www.python.org/ftp/python/3.6.3/Python-3.6.3.tgz
tar xvf Python-3.6.3.tgz
cd Python-3.6.3
./configure --enable-optimizations
make -j8
sudo make altinstall
python3.6

 

Install pip

wget https://bootstrap.pypa.io/get-pip.py
sudo python get-pip.py

 

WebSocket 

websockets requires Python ≥ 3.4. Install it with:

pip install websockets

async and await aren’t available in Python < 3.5. Here’s how to adapt the client example for older Python versions.

http://websockets.readthedocs.io/en/stable/intro.html

Function

Pass by Reference vs Value

All parameters (arguments) in the Python language are passed by reference. It means if you change what a parameter refers to within a function, the change also reflects back in the calling function. 

#!/usr/bin/python3

# Function definition is here
def changeme( mylist ):
   "This changes a passed list into this function"
   print ("Values inside the function before change: ", mylist)
   mylist[2]=50
   print ("Values inside the function after change: ", mylist)
   return

# Now you can call changeme function
mylist = [10,20,30]
changeme( mylist )
print ("Values outside the function: ", mylist)

Compare to this:

#!/usr/bin/python3

# Function definition is here
def changeme( mylist ):
   "This changes a passed list into this function"
   mylist = [1,2,3,4] # This would assi new reference in mylist
   print ("Values inside the function: ", mylist)
   return

# Now you can call changeme function
mylist = [10,20,30]
changeme( mylist )
print ("Values outside the function: ", mylist)

 

Global vs. Local variables

Variables that are defined inside a function body have a local scope, and those defined outside have a global scope.

total=0
def sum(arg1,arg2):
    total=arg1+arg2
    print("Inside the function local total: ",total)
    return total

sum(10,20)
print("Outside the function global total: ",total)

Results:

D:\home\training\PytonTutorial
λ python.exe functionPractice.py
Inside the function local total:  30
Outside the function global total:  0

Compare to another one:

'

total=0
def sum(arg1,arg2):
    global total
    total=arg1+arg2
    print("Inside the function local total: ",total)
    return total

sum(10,20)
print("Outside the function global total: ",total)

Results:

D:\home\training\PytonTutorial
λ python.exe functionPractice.py
Inside the function local total:  30
Outside the function global total:  30

 

Reference:

1. How to install python3.6, https://unix.stackexchange.com/questions/332641/how-to-install-python-3-6
2. websocket, http://websockets.readthedocs.io/en/stable/intro.html
3. RTD