- Running a Python program from the command line
- The main entry point
- Importing standard libraries, third-party libraries, and our own code
- Command Line Arguments
- Branching with the if, elif, and else statements
- Looping/Iteration with the for statement
- Environment Variables
- Exception Handling with the try and except statements
- Ignore the exceptions with the pass statement in this example program
- Built-in functions - float() and sorted()
- Invoking HTTP GET requests synchronously and asynchronously with the httpx library
- Synchronous and Asynchronous Programming
- Common Built-in Datatypes you'll use in every program:
- str - string values (text values, such as "Hello, World!")
- int - integer numbers
- float - floating-point numbers
- dict - dictionary, a set of key-value pairs, such as os.environ
- list - an array of sequential values, such as sys.argv
- Indentation matters in Python
- It must be properly indented or you'll get an error at runtime
This session uses file main-cli-sample.py as our Python CLI program.
Python is a relatively simple language, and this sample program goes far in demonstrating the core concepts of the language.
No! Learn at your own pace, in time. Please absorb what you can now.
Resource like the following can be helpful.
Let's execute it to ask it for help.
python main-cli-sample.py help
It responds with:
Usage:
python main-cli-sample.py <func>
python main-cli-sample.py add_numbers 1 2 3 4 5
python main-cli-sample.py add_numbers_better 1 2 3 4 oops 5
python main-cli-sample.py print_environment_variables
python main-cli-sample.py download_openflights_airports
python main-cli-sample.py download_openflights_airports_async
Options:
-h --help Show this screen
--version Show version
The program uses the docopt library for this.
It's important give users of your program instructions on how to use it.
We define our help content in a multi-line string comment at the top of the file.
Python multi-line string values begin with three double quotes (""") and end with three double quotes (""").
These topics are best described by walking through the the code and executing it.
python main-cli-sample.py add_numbers 1 2 3 4 5
sys.argv: ['main-cli-sample.py', 'add_numbers', '1', '2', '3', '4', '5']
1
2
3
4
5
The total is 15.0
Let's try it with an invalid number.
python main-cli-sample.py add_numbers 1 2 3 4 oops 5
sys.argv: ['main-cli-sample.py', 'add_numbers', '1', '2', '3', '4', 'oops', '5']
1
2
3
4
oops
could not convert string to float: 'oops'
Traceback (most recent call last):
File "/Users/cjoakim/github/zero-to-AI-private/python/main-cli-sample.py", line 100, in <module>
add_numbers()
~~~~~~~~~~~^^
File "/Users/cjoakim/github/zero-to-AI-private/python/main-cli-sample.py", line 46, in add_numbers
n = float(arg) # convert the command line string value to a floating-point number
ValueError: could not convert string to float: 'oops'
python main-cli-sample.py add_numbers_better 1 2 3 4 oops 5
1
2
3
4
oops
5
The total is 15.0
oops is not a number, so it is ignored.
The try/except statement is used to catch exceptions, and either handle or ignore them.
Display the environment variable names on your system, or in the .env file, in sorted order with the sorted() built-in function.
python main-cli-sample.py print_environment_variables
...
AZURE_COSMOSDB_EMULATOR_ACCT
AZURE_COSMOSDB_EMULATOR_KEY
AZURE_COSMOSDB_EMULATOR_URI
AZURE_COSMOSDB_NOSQL_ACCT
AZURE_COSMOSDB_NOSQL_AUTHTYPE
AZURE_COSMOSDB_NOSQL_CONN_STR
AZURE_COSMOSDB_NOSQL_KEY
AZURE_COSMOSDB_NOSQL_URI
...
Create or edit the .env file in the python directory, and run this again. You should see the your new environment variable(s).
This uses the httpx library to invoke an HTTP GET request to the OpenFlights API.
python main-cli-sample.py download_openflights_airports
python main-cli-sample.py download_openflights_airports | head
response: <Response [200 OK]>
response.status_code: 200
response.text: 1,"Goroka Airport","Goroka","Papua New Guinea","GKA","AYGA",-6.081689834590001,145.391998291,5282,10,"U","Pacific/Port_Moresby","airport","OurAirports"
2,"Madang Airport","Madang","Papua New Guinea","MAG","AYMD",-5.20707988739,145.789001465,20,10,"U","Pacific/Port_Moresby","airport","OurAirports"
3,"Mount Hagen Kagamuga Airport","Mount Hagen","Papua New Guinea","HGU","AYMH",-5.826789855957031,144.29600524902344,5388,10,"U","Pacific/Port_Moresby","airport","OurAirports"
...
14108,"Krechevitsy Air Base","Novgorod","Russia",\N,"ULLK",58.625,31.385000228881836,85,\N,\N,\N,"airport","OurAirports"
14109,"Desierto de Atacama Airport","Copiapo","Chile","CPO","SCAT",-27.2611999512,-70.7791976929,670,\N,\N,\N,"airport","OurAirports"
14110,"Melitopol Air Base","Melitopol","Ukraine",\N,"UKDM",46.880001,35.305,0,\N,\N,\N,"airport","OurAirports"
This program was formatted using the ruff program.
It's good to use a standard code style on your projects as it enhances readability and reduces team friction.
ruff format main-cli-sample.py
1 file reformatted
The complete program is shown below:
"""
Usage:
python main-cli-sample.py <func>
python main-cli-sample.py add_numbers 1 2 3 4 5
python main-cli-sample.py add_numbers_better 1 2 3 4 oops 5
python main-cli-sample.py print_environment_variables
python main-cli-sample.py download_openflights_airports
python main-cli-sample.py download_openflights_airports_async
Options:
-h --help Show this screen
--version Show version
"""
# The above content is so that the docopt library can display command-line help
# regarding how to run this program.
# Import statements are used to load the necessary standard libraries,
# third-party libraries, and our own code into the program.
# These are typically in this sequence - standard libraries, third-party libraries, our own code.
import os # standard library for operating system-related functions
import sys # standard library for system-related functions
import traceback # standard library for traceback functions
import asyncio # pythonlibrary for asynchronous programming (async/await)
import httpx # python library for HTTP requests
from docopt import docopt
from dotenv import load_dotenv # from the dotenv library use the load_dotenv function
from src.io.fs import (
FS,
) # class FS is in the src/fs.py file, our own code for filesystem operations
def print_options():
arguments = docopt(__doc__, version="1.0.0")
print(arguments)
def add_numbers():
total = 0.0
print(f"sys.argv: {sys.argv}") # print the command line arguments
for arg in sys.argv[2:]: # iterate the command line arguments, ignoring the first two
print(arg) # print the command line argument
n = float(arg) # convert the command line string value to a floating-point number
total = total + n # float() is one of the Python built-in functions
print(f"The total is {total}")
def add_numbers_better():
total = 0.0
for arg in sys.argv[2:]:
print(arg)
try:
n = float(arg)
total = total + n
except Exception as e: # "catch any exceptions"
pass # ignore the non-numeric arguments provided on the command line
print(f"The total is {total}")
def print_environment_variables():
env_var_names = sorted(os.environ.keys()) # get a sorted list of the environment variable names
for name in env_var_names:
print(f"{name}")
# print(f"{name}: {os.environ[name]}")
def openflights_airports_url() -> str:
# See https://openflights.org/data#airport
return "https://raw.githubusercontent.com/jpatokal/openflights/master/data/airports.dat"
def download_openflights_airports():
# This is a synchronous HTTP GET request
url = openflights_airports_url()
response = httpx.get(url)
print(f"response: {response}")
print(f"response.status_code: {response.status_code}")
print(f"response.text: {response.text}")
async def download_openflights_airports_async():
# This is an asynchronous HTTP GET request
# Several languages use the "async/await" syntax to write asynchronous code
async with httpx.AsyncClient() as client:
response = await client.get(openflights_airports_url())
print(f"Status Code: {response.status_code}")
print(f"Content Type: {response.headers['content-type']}")
print(response.text)
if __name__ == "__main__": # __main__ is execute when the program is run from the command line
try:
load_dotenv(override=True) # load the .env file into the environment
func = sys.argv[1].lower() # get the function name from the command line
# sys.argv is a list of command line arguments
if func == "add_numbers":
add_numbers()
elif func == "add_numbers_better":
add_numbers_better()
elif func == "print_environment_variables":
print_environment_variables()
elif func == "download_openflights_airports":
download_openflights_airports()
elif func == "download_openflights_airports_async":
asyncio.run(download_openflights_airports_async())
else:
print_options()
except Exception as e:
print(str(e)) # print the error message
print(traceback.format_exc()) # print the traceback, or stack trace
- Just type "python" in your project (with virtual environment activated)
- Type python code line-by-line
- See the output of the code as you type it
- Enter "exit()" and the Enter key when you're done
Ask your AI assistant in your IDE (i.e. - Cursor, VSC, etc.) to explain the code.
Prompt:
In file main-cli-sample.py, what does "sys.argv[2:]" mean on line 46?
Do you remember this from Session 0?
Prediction: You will learn more from AI (i.e. - Cursor) than from Chris