Python Programming: Scripting

Lesson Objectives

After this lesson, you will be able to…

Explain the uses of scripting.
Write scripts that perform file I/O.
Write scripts that take user input.

Introduction

Discussion: What comes to mind when you hear the word “scripting”?

What’s a Scripting Language?

There are only two types of programming languages in the world: scripting languages or compiled languages.

All languages, like Python, are one of these two categories.

Scripting languages:

One is Python!
Write code, then immediate run it: python my_file.py
Executes statements in order.
Find a bug? Fix it, run it, repeat.

What’s a Scripting Language?

Compiled languages:

Compile means “build”.
We can’t immediate run code - the computer can’t just read the code and needs to translate it to something it understands first.
Write code, then compile it (not quick!), then run it.
Find a bug? Fix it, wait for the code to compile, run it, repeat.

You don’t need to memorize this - just know that there’s a difference, and Python is scripting.

What do you think a script is?

Teaching Tips:

It’s not important for them to memorize what compiled is - just get the idea that it’s a different kind of language.

Talking Points:

A scripting language or interpreted language like Python executes statements in order
A script is typically a file with some Python code in it
A script might calculate something, take input, give output, or do file I/O

All programming languages that exist in the world fall into one of two buckets. A scripting language or interpreted language like Python executes statements in order. A compiled language needs to build your program before running it.

Imagine; you wrote an application with Java. Before you can run it, you need to compile it - turn it After compiling completed, you run your application. When running your application, you notice a bug. To fix it, you have to stop your application, go back to source code, fix the bug, wait for the code to recompile, and restart your application to confirm that it is fixed. And if you find another bug, you’ll need to repeat that process again.

In a scripting language, you can fix the bug and just need to reload your application —no need to restart or recompile anymore. It’s as simple as that.

Technically, you’ve been writing scripts already.

What is a Script?

Just some code that does something.

Usually written in a scripting language.
Can be as simple or as complex as needed!

Let’s write a script:

Create a file called my_script.py
Open the file in Atom.
Type the line

print("hello world!")

CONGRATS: You now have a script!

Look familiar? You’ve been scripting since day 1!

Scripting, Commonly

When people say scripts, though, they usually mean code that:

Takes input.
Gives output.
Reads or writes to a file.
Performs a task.

We have “perform a task” down!

Quick Review

Script:

Just code that does something. You’ve written dozens of scripts in Python so far!

Scripting Language:

A language where you can immediately run code. Python is one!
Write -> Run.

Compiled Language:

Compile means build! We can’t immediately run code.
Write -> Build -> Run.

We’re only working with Python, so we can just write and run our code!

Next Up: Playing with files in Python.

Scripting, Part 1: Files

Let’s further our programming toolkit.

On your computer, you can:

Create or open a file (text, jpg, Word doc…).
Read it.
Edit it.
Close it.

These are pretty basic actions. Can we do it in Python?

We Do: Let’s Read a File!

With files, there are three key points.

Tell Python to open the file: my_file = open(<file name>)
Do something with the file! (Read it, edit it, etc).
Close the file when you’re done: my_file.close()

First, let’s check out read: View, but not change, the contents, with read().

Let’s try. On your Desktop, create a file called “hello.txt” with the word “hi” in it.

Now, also on your Desktop, create a file, first_reading.py. Fill it with: python my_file = open("hello.txt") print(my_file.read()) my_file.close()
Run it!

Note: The file must exist already!

What About Editing Files?

In programming, “edit” is referred to as “write”, short for “write to.” How do we write a file?

open(<file name>) has optional parameters: open(<file name>, <mode>)

Mode: “What do you want to do with the file?” The default is “read.” Use w for “write”:

# To read a file:
my_file = open("hello.txt")
print(my_file.read()) ## We want this to be write, not read!
my_file.close()

# To write a file:
my_file = open("hello.txt", "w")
## Write some stuff
my_file.close()

Important: Write overwrites the current file!

We Do: Writing Files

Let’s try this. Change your script. We’re going to make it a little more complex - since we’re programming, we can use variables!

# Open the file hello.txt
my_file = open("hello.txt", "w")

# Write some content to my_file.txt
my_file.write("Hello world")
my_text = "Apple juice is delicious." # Use the variable!
my_file.write(my_text) # Writes "Apple juice is delicious."
my_file.write("Have a nice day!")

# Always close the file
my_file.close()

Run it!

Open the file to check.

Thought: How could you make new lines?

Discussion: Writing Complex Strings

What happens if we try to write multiple strings?

# But it doesn't  work with write.
my_file = open("a_file.txt", "w")
my_text = "Apple juice is delicious."
my_file.write(my_text, "Don't you think?") # Error! Write takes 1 argument (2 given).

my_file.close()

Error! write only takes one argument. We need to concat the strings. Always just pass one argument to file.write().

my_file = open("a_file.txt", "w")
my_text = "Apple juice is delicious."
string_to_write = my_text + "Don't you think?" # Make one string here!
my_file.write(string_to_write)
my_file.close()

We Do: Creating Files

What if the file doesn’t exist yet?

Write to the rescue!

Write opens a file for writing…
But it also creates it if need be!

At the bottom of your script, add:

# Open OR create file totally_new_file.txt
my_new_file = open("totally_new_file.txt", "w")

# Write some content to totally_new_file.txt
my_new_file.write("Content goes here")

# Always close the file
my_new_file.close()

Check your desktop after running it!

You Do: Create a File

Now, try it yourself. Write a new script:

open(), in read mode, your existing a_file.txt.
.read() the file and save the contents into a variable, file_contents.
Using .write(), create a new file called b_file.txt.
Write file_contents to b_file.txt.

Don’t forget to close() your files!

Create a File: Solution

my_file = open("a_file.txt", "r")
file_contents = my_file.read()
my_file.close()

my_file_script = open("b_file.txt", "w")
my_file_script.write(file_contents)
my_file_script.close()

Teaching Tips:

After they do this, show it to them. Show them opening multiple files at the top, too, so they know you don’t have to go sequentially: e.g.

file_to_read = open("a_file.txt")
file_to_write = open("b_file.txt", "w")


file_contents = file_to_read.read()
file_to_write.write(file_contents)

file_to_read.close()
file_to_write.close()

Quick Review

You can open, read, and write files with Python.

Write will create the file if it doesn’t already exist.

Always close your files!

file_to_read = open("a_file.txt")
file_to_write = open("my_file_script.txt", "w")


string_to_write = file_to_read.read()
file_to_write.write(string_to_write)

file_to_read.close()
file_to_write.close()

Next up: More advanced file options.

Other File Modes

What if we want to read AND write a file? Or write to the end of a file instead of overwriting what’s there?

open has a few other modes.

Value	Mode	Purpose
`r`	Reading	Read only. The default!
`w`	Write	Use to change (and create) file contents
`a`	Append	Use to write to the end of a file
`r+`	Read Plus	Can do both read and write

Don’t memorize this; just know it’s there. A lot of programming is understanding your options and then Googling the syntax! The biggest thing for you to learn is the concepts that Python can do.

Teaching Tips:

Stress that this is a lot to take in and they don’t need to remember it all. We’re practicing for their understanding, not their memorization. (Also, the more we practice, the more likely they’ll just remember it).
Show r+ and a. You can work off this basic code:

# Open the file hello.txt
my_file = open("hello.txt", "w")
my_file.read() # Error! Not readable.
my_file.write("hey")
# Close the file
my_file.close()

I Do: The With Keyword

Always remembering to close a file can be hard. There’s another way to open files so Python closes it for us!

# Instead of:
file_object = open("my_file.txt", "w")
file_object.write("Hello World!")
file_object.close()

# We can say:
with open("my_file.txt", "w") as file_object: # This line replaces the open and close above
  file_object.write("Hello World!") # This line is the same; note the indent!

What Else is in File?

These are just for reference - we won’t be using them!

Do you have a list that you want to write on multiple lines? Use my_file.writelines([<your list>])
Does your file have things on multiple lines you want to read into a list variable? Use list_contents = my_file.readlines()
Separating some written lines? Add \n to the write()

Quick Review:

File has a lot of advanced options.

You can write a list across multiple lines, or read a file with multiple lines into a list variable.
Write only takes one argument, so concat your strings!
You can open files using with to automatically close them.

# Instead of:
file_object = open("my_file.txt", "w")
file_object.write("Hello World!")
file_object.close()

# We can say:
with open("my_file.txt", "w") as file_object: # This line replaces the open and close above
  file_object.write("Hello World!") # This line is the same; note the indent!

Next up: User Input!

What about User Input?

We’ve just done a lot with file I/O (in/out).

We can prompt users for information, too.

You’ve seen this a few times (remember the error checking, with the try/catch?)! It’s very common.

# Prompts with "input"
# Saves result in user_name
user_name = input("Please type your name:")

You Do: Bring it all Together!

Create a file called about_script.py.
In it, prompt the user for their name. Then, prompt them for their favorite food.
Using write, create a file called about_me.txt.
In about_me.txt, write out the name and favorite food in a sentence.

Bonus: Use format for forming your sentence!

Bring it all Together, Solution

user_name = input("Please type your name: ")
user_food = input("Please type your favorite food: ")

file = open("about_me.txt", "w")
file.write("My name is " + user_name +  " and my favorite food is " +  user_food)

Summary and Q&A

Scripting language vs compiled language.

Scripting languages: Write -> Run.
Compiled languages: Write -> Build -> Run.

Script:

Just some code!

Summary and Q&A

File I/O:

my_file = open("a_file.txt", "w")
my_file.write("Some content")
my_file.write(my_text)
my_file.close()

User input

user_name = input("Please type your name:")

Python Programming: Scripting

Lesson Objectives

Introduction

What’s a Scripting Language?

What’s a Scripting Language?

What is a Script?

Scripting, Commonly

Quick Review

Scripting, Part 1: Files

We Do: Let’s Read a File!

What About Editing Files?

We Do: Writing Files

Discussion: Writing Complex Strings

We Do: Creating Files

You Do: Create a File

Create a File: Solution

Quick Review

Other File Modes

I Do: The With Keyword

What Else is in File?

Quick Review:

What about User Input?

You Do: Bring it all Together!

Bring it all Together, Solution

Summary and Q&A

Summary and Q&A

Additional Resources