Week 1: Introduction to CS21 and Python Programming
Week 1 Goals
-
Understand course format and policies
-
Learn about the CS network and Linux
-
Learn to use the Visual Studio Code editor (
code
) -
Learn how to write and run python programs
-
Learn basic python syntax and semantics
-
Learn the
string, integer, and float
data types
Course Overview
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Login with CS account. Reset your Password if needed.
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Open your browser and bookmark the course webpage https://www.cs.swarthmore.edu/courses/CS21/F24/
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Review the course syllabus
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Read Lab 0 before lab.
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Attend Lab
-
This course has a final exam. Do not schedule end of semester travel plans until we know the final exam time (scheduled by the Registrar)
Get Week 1 In-class Code
To copy over the week 1 in-class example programs, do the following (If you have trouble with either of these steps, ask a Ninja or your professor for help):
-
Create a w01-intro subdirectory in your
cs21/inclass
directory, and cd into it:$ cd ~/cs21/inclass $ mkdir w01-intro $ cd w01-intro $ pwd /home/yourusername/cs21/inclass/w01-intro
-
Copy over the week 1 files into your
w01-intro
subdirectory (check that they copied successfully copied by runningls
:$ cp ~admin21/public/w01-intro/*.py ./ $ ls greeting.py numbers.py welcome.py
Editing and Running Python programs
To open and edit a Python source code file, in a terminal, run the
code
editor with the name of the file you want to edit (e.g., prog.py
):
$ code prog.py
To run a Python program, in a terminal, invoke the Python
interpreter (python3
) followed by the name of the file with the
Python program you want to run (e.g. prog.py
):
$ python3 prog.py
Week 1 Code
welcome.py
The welcome.py
program shows an example Python program.
Let’s open it in code
and look at some of the main features
of a Python program:
$ code welcome.py
Now, lets run the program using the Python interpreter. In a terminal window type:
$ python3 welcome.py
greeting.py
Open greeting.py
with code
and try running it with python. Let’s try to modify the program
to prompt the user for a different greeting.
numbers.py
-
numbers.py
introduces a second data type: integer. What was the first data type we saw? -
Modify
numbers.py
to cast the user input to a float. Save, run, and test your program. -
You can also use the python shell to try small examples. Type
python3
in a terminal without a file name to enter the shell. TypeCtrl-D
to exit the shell. Note the>>>
prompt for the python shell. -
Try a few operations in the shell
>>> txt = "hello" >>> a = 2 >>> x = 3.5 >>> type(txt) >>> type(a) >>> type(x) >>> x + a >>> a + txt >>> txt + txt >>> ans = "2.7" >>> y = float(ans) >>> print(y) >>> type(y) >>> b = int(y) >>> type(b) >>> print(b) >>> c = int(ans)