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Tips

Find all installed modules
help("modules");
Virtual Environment

With virtualenv and virtualenvwrapper

# Installing virtualenv and virtualenvwrapper
sudo pip install virtualenv virtualenvwrapper

# Update the profile ~/.bashrc
# Add the  following lines

# Python virtualenv and virtualenvwrapper
export WORKON_HOME=$HOME/.virtualenvs
export VIRTUALENVWRAPPER_PYTHON=/usr/bin/python3
source /usr/local/bin/virtualenvwrapper.sh

# Reload the profile
source ~/.bashrc

# Creating python virtual environment
# The py3cv3 is a self-defined name 
mkvirtualenv py3cv3 -p python3

# Enter the specified virtual environment
workon py3cv3

# Exit the the specified virtual environment
deactivate

# List all of the environments.
lsvirtualenv

# Remove an environment
rmvirtualenv py3cv3
Timestamp
timestamp = datetime.datetime.now()
print("It is {}".format(timestamp.strftime("%A %d %B %Y %I:%M:%S%p")))
Math
total += 1
If-then
# Boolean, none
if motion is not None:
if not flag:

# Number
if delay > 0:
if delay == 0:
if total > frameCount:

# String
if "blue" in style:
if authors.startswith('['):
    authors = authors.lstrip('[').rstrip(']')
    
def doi_url(d): return f'http://{d}' if d.startswith('doi.org') else f'http://doi.org/{d}'
Command Arguments
# construct the argument parser and parse the arguments
ap = argparse.ArgumentParser()
ap.add_argument("-i", "--interval", required=False,
        help="Seconds to Interval (Default:30)", default="30", type=int)
ap.add_argument("-o", "--output", required=False,
        help="Path to Output Logs (Default:std-out)")
args = vars(ap.parse_args())

# Usage
intv = args["interval"]
logfile = args["output"]
JSON

JSON to dict

json.loads 用來轉換資料; json.load 用來讀檔。

import json

person = '{"name": "Bob", "languages": ["English", "French"]}'
person_dict = json.loads(person)

# Output: {'name': 'Bob', 'languages': ['English', 'French']}
print( person_dict)

# Output: ['English', 'French']
print(person_dict['languages'])

Dict to JSON

import json

person_dict = {'name': 'Bob',
'age': 12,
'children': None
}
person_json = json.dumps(person_dict)

# Output: {"name": "Bob", "age": 12, "children": null}
print(person_json)

Read JSON file

import json

with open('path_to_file/person.json', 'r') as f:
  data = json.load(f)

# Output: {'name': 'Bob', 'languages': ['English', 'French']}
print(data)

Write JSON file

json.dump 用來寫檔案; json.dumps 用來轉換資料。

import json

person_dict = {"name": "Bob",
"languages": ["English", "French"],
"married": True,
"age": 32
}

with open('person.txt', 'w') as json_file:
  json.dump(person_dict, json_file)

Print JSON

import json

person_string = '{"name": "Bob", "languages": "English", "numbers": [2, 1.6, null]}'

# Getting dictionary
person_dict = json.loads(person_string)

# Pretty Printing JSON string back
print(json.dumps(person_dict, indent = 4, sort_keys=True))

Access JSON

import json

json_data = '''
{
    "students": [
        {
            "name": "David",
            "age": 19,
            "grades": {
                "math": 90,
                "english": 87
            }
        },
        {
            "name": "Harry",
            "age": 21,
            "grades": {
                "math": 85,
                "english": 95
            }
        }
    ]
}
'''

# Parse JSON Data
data = json.loads(json_data)

# To access a large dataset we can use `for loop`
for student in data["students"]:
    name = student["name"]
    math_mark = student["grades"]["math"]
    english_mark = student["grades"]["english"]
    average_mark = (math_mark + english_mark) / 2
    print(f"{name}, Avarage Marks: {average_mark:.2f}")


# Output:
# David, Average Marks: 88.50
# Harry, Average Marks: 90.00
import json

original_data_file="students_data.json"
updated_data_file="students_data_updated.json"

# reading `JSON file`
with open(original_data_file,"r") as file:
   students_result = json.load(file)

# Updating JSON Data
for student in students_result['students']:
    print(student['name'])
    
    if student['name'] == "Kabir":
        student['name'] = "John"
        
    grades = student['grades']
    avarage_mark= sum(grades.values()) / len(grades)
    student['avarage_mark'] = avarage_mark

# Saving updated data into a new file
with open(updated_data_file,"w") as file:
    json.dump(students_result,file,indent=4)

Get JSON from URL

import requests, json

# Response will be saved here
weather_data="weather_data.json"

# Request to `openweathermap` API
api_key = "6423af6e554f98cf1e6b8c6a7700986b"   #REPLACE_WITH_YOUR_API_KEY
location = "Dhaka"
url = f"https://api.openweathermap.org/data/2.5/weather?q={location}&appid={api_key}&units=metric"

# Response
response = requests.get(url)

# Get `Place` and `Temperature` from the Response
if response.status_code == 200:
    json_data = response.json()
    print(f"Place: {json_data['name']}, Temperature: {json_data['main']['temp']} celsius")
else:
    print(f"Request failed with status code {response.status_code}")

# Save the Response to a file
with open(weather_data,"w") as file:
       json.dump(json_data,file,indent=4)


# Output:
# Place: Dhaka, Temperature: 27.99 celsius
# Handling a JSONDecodeError in Python
from json import JSONDecodeError
import requests
resp = requests.get('https://reqres.in/api/users/page4')
try:
    resp_dict = resp.json()
except JSONDecodeError:
    print('Response could not be serialized')

Data Type

使用 json.loads 轉換資料型別時，要注意輸出的類型可能是 dict 或者 array，這要看原始JSON 的資料格式。

JSON
 Python
object
 dict
array
 list
string
 str
number (integer)
 int
number (real)
 float
true
 True
false
 False
null
 None 
import json

country = '{"name": "United States", "population": 331002651}'
country_dict = json.loads(country)

print(type(country))
print(type(country_dict))

# Output:
# <class 'str'>
# <class 'dict'>
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