Day #1 - Simple Python projects
print("Hello, World!")
What is Python?
Python is a popular programming language. It was created by Guido van Rossum, and released in 1991.
It is used for:
- web development (server-side),
- software development,
- mathematics,
- system scripting.
What can Python do?
- Python can be used on a server to create web applications.
- Python can be used alongside software to create workflows.
- Python can connect to database systems. It can also read and modify files.
- Python can be used to handle big data and perform complex mathematics.
- Python can be used for rapid prototyping, or for production-ready software development.
Why Python?
- Python works on different platforms (Windows, Mac, Linux, Raspberry Pi, etc).
- Python has a simple syntax similar to the English language.
- Python has syntax that allows developers to write programs with fewer lines than some other programming languages.
- Python runs on an interpreter system, meaning that code can be executed as soon as it is written. This means that prototyping can be very quick.
- Python can be treated in a procedural way, an object-oriented way or a functional way.
To check if you have python installed on a Windows PC, search in the start bar for Python or run the following on the Command Line (cmd.exe):
C:\\Users\\_Your Name_\>python --version
To check if you have python installed on a Linux or Mac, then on linux open the command line or on Mac open the Terminal and type:
python --version
As we learned in the previous page, Python syntax can be executed by writing directly in the Command Line:
>>> print("Hello, World!")
Hello, World!
Or by creating a python file on the server, using the .py file extension, and running it in the Command Line:
C:\Users\Your Name>python myfile.py
Creating a Comment
Comments starts with a #, and Python will ignore them:
#This is a comment
print("Hello, World!")
Creating Variables
Python has no command for declaring a variable.
A variable is created the moment you first assign a value to it.
x = 5
y = "John"
print(x)
print(y)
Variable Names
A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume). Rules for Python variables:
- A variable name must start with a letter or the underscore character
- A variable name cannot start with a number
- A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
- Variable names are case-sensitive (age, Age and AGE are three different variables)
- A variable name cannot be any of the Python keywords.
Global Variables
x = "awesome"
def myfunc():
print("Python is " + x)
myfunc()
x = "awesome"
def myfunc():
x = "fantastic"
print("Python is " + x)
myfunc()
print("Python is " + x)
x = 1 # int
y = 2.8 # float
z = 1j # complex
#convert from int to float:
a = float(x)
#convert from float to int:
b = int(y)
#convert from int to complex:
c = complex(x)
print(a)
print(b)
print(c)
print(type(a))
print(type(b))
print(type(c))
Random Number
import random
print(random.randrange(1, 10))
_An interesting example of Slicing:
_
explain b = "Hello, World!"
print(b[-5:-2])
- Variable Assignment:
python
b = "Hello, World!"
This line assigns the string "Hello, World!" to the variable b.
- String Slicing:
python
print(b[-5:-2])
This line prints a slice of the string b. Here's how the slicing works:
- Negative Indexing: In Python, negative indices count from the end of the string. So,
-1is the last character,-2is the second last, and so on. - Slice
b[-5:-2]: This means "start from the 5th character from the end and go up to (but not including) the 2nd character from the end."
Let's visualize the string with indices:
H e l l o , W o r l d !
0 1 2 3 4 5 6 7 8 9 10 11 12
-13-12-11-10 -9 -8 -7 -6 -5 -4 -3 -2 -1
So, b[-5:-2] corresponds to the characters orl from the string "Hello, World!".
Therefore, the output of print(b[-5:-2]) will be:
orl
Python Strings
Top comments (2)
Keep up the fantastic work!
Brilliant. It's an amazing detail of Python 💯