Strings & Input/Output

# Strings & Input/Output

Week 3

---

## Review

![](https://media0.giphy.com/media/v1.Y2lkPTc5MGI3NjExZnFyNnFsYXBmM21wdGdmbm5uMGFtbTEyNHRjaHhheXczbDJ1NzlvcSZlcD12MV9pbnRlcm5hbF9naWZfYnlfaWQmY3Q9Zw/a5viI92PAF89q/giphy.gif)

### How do computers store text?

Binary (numbers)

### What is a single binary digit called?

Bit

### How many bits in a byte?

8

### What is a variable?

A name for some data

### Can the value in a variable change?

Yes!

It's called "re-assignment"

### Types of _primitive_ values?

- Integer (int) 
- Floating Point Number (float) 
- String (str) 
- Boolean (bool) 
- NoneType (None)

### Types of _compound_ values?

- Lists 
- Tuples 
- Dictionaries 
- Sets

NOTE: the two that matter for this class are **lists** and **dictionaries**

---

## I/O (Input and Output)

### Types of Input

How can you give information **TO** a computer?

![vintage computer keyboard](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fi.redd.it%2F0doy19w3wta91.jpg&f=1&nofb=1&ipt=47d4360ea7035a85ad9abbfa219659e6a27d39395bca2d3e1115dcd69cdc2f90)

![fingerprint sensor](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fwww.notebookcheck.net%2Ffileadmin%2FNotebooks%2FNews%2F_nc3%2Fxps_13_2_in_1_ces_2017_6_2_1500x1000.jpg&f=1&nofb=1&ipt=09408637b09dca8a95a1b29852b271e9731e28298fa5e01672380aed708628fa)

![MouthPad](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fwww.maglazana.com%2Fwp-content%2Fuploads%2F2023%2F04%2FMouthPad_Product_01.jpg&f=1&nofb=1&ipt=3da77ff0f64085d6a48645ca508d52a1d52c42bdfb81d22afb726a3e11c7c52f)

### Types of Output

How can you get information **FROM** a computer?

![CRT computer monitor](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fonthenode.com%2Fwp-content%2Fuploads%2F2024%2F09%2F6d577e4a-0fc0-4715-8e3b-cb03861a79b3_4032x3024-scaled.jpg&f=1&nofb=1&ipt=0a67ed3b47f4c5afdc85354cbc8eb53361f87759f58a22e0b4635f956659fa23)

NOTE: not all computers have a screen!

![car interior](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fhips.hearstapps.com%2Fhmg-prod%2Fimages%2Frp-bentley-continental-gt-v8-20-2-1570633139.jpg&f=1&nofb=1&ipt=794fe599994704b9b3b46f279cedc1a9d6f3ca0bf52f80733276035d44ab00f0)

![braille display](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fuploads-ssl.webflow.com%2F65b8ddcbf33493a2084590af%2F66275dee46f8ce441ee3eb58_braille%2520display%2520with%2520tactile%2520cells%2520how%2520to%2520choose%2520a%2520braille%2520display.jpg&f=1&nofb=1&ipt=bf933f37e489a88b712506bb082607ba1b0e9f17683fe1d7cb47803c1f6cfe08)

---

## Terminals

> A "terminal" allows you interact with the computer using text

![Windows Command Prompt](https://www.lifewire.com/thmb/WMnxws1Vb530hxMS5etjP4oX9OM=/750x0/filters:no_upscale():max_bytes(150000):strip_icc()/command-prompt-1fcee7b9a02c4fbbab3c526964476c97.png)

A "console" is a physical I/O station

![Sage II vintage terminal](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fwww.vintagecomputer.net%2Fpictures%2F2011%2FSageII_Televideo_Pascal%2FUCSD_Pascal_Terminal9.jpg&f=1&nofb=1&ipt=b26cf9d9e1703d22e51eb3463723c3a9099e4132472d60a15793b86379b214a7)

A "shell" is a command interpreter

Essentially, the shell runs inside the terminal

A "command line interface" (abbreviated CLI) is a place to enter commands into a system

We'll try stick to <span class="green">terminal</span> or <span class="green">CLI</span>

NOTE: don't worry too much about the difference, just know the terms are often used interchangeably online

Programmers use terminals a LOT

Example: VPC

### Exercise: Use a Terminal Emulator

<h4><code>www.terminaltemple.com</code></h4>

---

## Printing

In Python, outputting text to terminal is called "printing"

![Teletype prints from WWII](https://upload.wikimedia.org/wikipedia/commons/8/89/WACsOperateTeletype.jpg?utm_source=en.wikipedia.org&utm_campaign=imageinfo&utm_content=thumbnail_unscaled)

### The `print()` function

```py
print("Hello, World!")
```

### Printing multiple values

```py
print("Hello,", "World!")
```

NOTE: print() automatically adds a space between comma-separated values

### What happens here?

```py
print(print)
```

NOTE: print() automatically adds a space between comma-separated values

---

## Input

### The `input()` function

```py
name = input("What is your name? ")
print("Hello, " + name)
```

```txt
What is your name? Rylan
Hello, Rylan
```

NOTE:
- input() always returns a string, even if the user types a number
- How is input stored? A **variable**

### What's wrong here?

```py
age = input("How old are you? ")
print(age + 1)
```

```txt
TypeError: can only concatenate str (not "int") to str
```

### Converting to a number

```py
age = input("How old are you? ")

# Convert string to integer
age = int(age)

print(age + 1)
```

## Exercise

Write a program that asks the user a question, processes the input, and prints a response

NOTE: Try processing different data types (not just strings)

---

## Working with Strings

### Concatenation

Joining strings together with `+`

```py
first_name = "Ada"
last_name = "Lovelace"
full_name = first_name + " " + last_name
print(full_name)
```

### String Formatting (f-strings)

```py
name = "Ada"
age = 28
print(f"{name} is {age} years old")
```

NOTE: f-strings let you insert variables directly into a string

### Formatting decimals

Use `:.Nf` to show **N** digits after the decimal

```py
pi = 3.1415926535
print(f"{pi:.2f}")
print(f"{pi:.4f}")
```

```txt
3.14
3.1416
```

NOTE:
- `.2f` is common for money
- Python **rounds**, it does not just chop digits off
- `f` means "fixed-point" (a decimal number)

### Money example

```py
price = 4.5
print(f"That costs ${price:.2f}")
```

```txt
That costs $4.50
```

### Padding (width)

Put a number after the colon to set a **minimum width**

```py
word = "hi"
print(f"|{42:5}|")
print(f"|{word:5}|")
```

```txt
|   42|
|hi   |
```

NOTE:
- Numbers are right-aligned by default
- Strings are left-aligned by default
- Extra spaces fill the unused width

### Alignment

- `<` left
- `>` right
- `^` center

```py
word = "hi"
print(f"|{word:<5}|")
print(f"|{word:>5}|")
print(f"|{word:^5}|")
```

```txt
|hi   |
|   hi|
| hi  |
```

### Zero-padding numbers

Useful for clocks, IDs, and columns that should line up

```py
hour = 9
minute = 5
print(f"{hour:02}:{minute:02}")
```

```txt
09:05
```

NOTE: `02` means "at least 2 digits, pad with zeros"

### Putting it together

```py
item = "apples"
price = 2.5
print(f"{item:<10} ${price:>6.2f}")
```

```txt
apples     $  2.50
```

NOTE: width and decimals can be combined: `>6.2f` means right-align in 6 characters, 2 decimal places

### Exercise

Create a program that does the following:

1. Ask user for a word or phrase
2. Ask user for width (n)
3. Print word inside frame _n_ characters wide

!["Carpe diem" in ASCII art](/2026/computer-science/images/carpe-diem-ascii-art.png)

```py
message = input("Enter a message: ")
width = input("Enter a width: ")
dash = '-'

line = f"*{dash:{dash}^{width}}*"
message = f"|{message:^{width}}|"

print()
print(line)
print(message)
print(line)
```

---

![Jimmy Fallon thats it](https://media4.giphy.com/media/v1.Y2lkPTc5MGI3NjExd2NmamM3NmR2c3RtenR3bGV5dnR1MnNyM3BzNnh3ZGNwYTFyZ2V6YyZlcD12MV9pbnRlcm5hbF9naWZfYnlfaWQmY3Q9Zw/uSZQ6WPIcpouUEpNTe/giphy.gif)