# **Python Input/Output (I/O)** In Python, handling data involves receiving information from the user (Input) and displaying results back to the user (Output). This is fundamental to creating interactive . ## **The `print()` Function** The `print()` function is the primary way to display output to the user in Python. It instructs the program to output whatever is placed inside its parentheses. - **Syntax:** `print("Your text or variable here")` - Text (known as a *string*) must be enclosed in quotes (`""` or `''`). - The function will display content exactly as it appears within the quotes, including leading or trailing spaces. ### **Advanced Print Parameters** Python's `print()` function includes optional parameters like `sep` (separator) and `end`. - **sep**: Specifies how to separate multiple objects in the same print statement. - **end**: Specifies what to print at the end of the statement (default is a newline `\n`). ### **Escape Sequences** Escape sequences are special characters used within strings to format output, such as moving to a new line or adding a tab space. - `\n`: Newline - `\t`: Horizontal Tab --- ## **The `input()` Function and Variables** Computer programs often need to process data entered by a user. The `input()` function is used to capture this data. - **Functionality:** It prompts the user for input and reads the line of text they enter. - **Storing Data:** The captured data is typically stored in a *variable* for later use. This prevents the user from having to enter the same information multiple times. **Example (Fig 3.13):** The user is prompted to enter a country name, which is stored in the `country` variable and then displayed using `print()`. ```python country = input("Enter a country name: ") print(country) ``` --- ## **Data Types and The `eval()` Function** The `input()` function always treats user input as a *string* (a set of characters), even if the user enters a number. This can cause problems with mathematical operations. - **String Concatenation:** When the `+` operator is used with strings, it joins them together. This process is called **concatenation**. For example, `"5" + "5"` results in `"55"`, not the number `10`. - **The `eval()` Function:** To perform mathematical calculations, string-based numbers must be converted into numerical types (*integer*, *float*). The `eval()` function evaluates a string expression and can be used to convert a numerical string into a number. Alternatively, `int()` or `float()` can be used for explicit conversion. **Example (Fig 3.14):** This diagram demonstrates the difference between adding inputs as strings versus adding them as numbers using `eval()`. | Code without `eval()` | Code with `eval()` | | :--- | :--- | | `num1 = input("Enter first number ")`
`num2 = input("Enter second number ")`
`sum = num1 + num2`
`print(sum)`
**Output (if user enters 10 & 20): 1020** | `num1 = eval(input("Enter first number "))`
`num2 = eval(input("Enter second number "))`
`sum = num1 + num2`
`print(sum)`
**Output (if user enters 10 & 20): 30** | --- ## **Practical Example: Date Formatting** Using the concepts above, you can take multiple inputs and format them. **Task:** Take three inputs (day, month, year) and print the date in different formats. ```python # Get input from the user day = input("Enter the day: ") month = input("Enter the month: ") year = input("Enter the year: ") # Print in different formats using f-strings print(f"{day}-{month}-{year}") print(f"{month}-{day}-{year}") print(f"{year}-{month}-{day}") ``` --- ## **Possible Questions/Answers** - **Q:** What is the difference between the `print()` and `input()` functions? **A:** The `print()` function displays information *to* the user (output), while the `input()` function receives information *from* the user (input). - **Q:** Why does `input()` sometimes cause issues with math? **A:** Because `input()` always captures data as a string. Using the `+` operator on two strings results in *concatenation* (joining them, e.g., "1" + "2" = "12") instead of mathematical addition (1 + 2 = 3). - **Q:** What is the purpose of the `eval()` function in this context? **A:** The `eval()` function is used to evaluate a string as a Python expression. When used with `input()`, it converts a string that looks like a number (e.g., "25") into an actual numerical data type (e.g., the integer 25), allowing it to be used in calculations. --- ## **Summary** - **Output:** Use `print()` to display text and variable values to the console. - **Input:** Use `input()` to get data from the user. The data is always returned as a string. - **Variables:** Store input data in variables to use it throughout a program. - **Type Conversion:** Since `input()` returns strings, functions like `eval()` (or `int()`, `float()`) are necessary to convert the string to a number before performing mathematical operations. - **Operators:** The `+` operator's behavior depends on the data type. | Data Type | `+` Operator Behavior | Example | | :--- | :--- | :--- | | *Numbers* (int, float) | Mathematical Addition | `10 + 20` results in `30` | | *Strings* (str) | Concatenation | `"10" + "20"` results in `"1020"` |