Differences Between Python 2 and 3
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Introduction to Input and Output in Python
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Today, we're going to talk about how Python interacts with its environment, focusing on standard input and output. Can anyone tell me what standard input is?
Is it when the program gets input from the keyboard?
Exactly! Standard input is typically from the keyboard. Now, what about standard output?
That's when the program displays output on the screen!
Right again! We use the `input()` function to read input and `print()` to display output. Let's remember that 'I' stands for input and 'P' for print. Can anyone tell me how the `input()` function behaves?
It waits for the user to enter something and then stores it in a variable.
Correct! It captures a line of input and returns it as a string. Good job!
So, how do we display a prompt for the user?
Great question! You can add a string as an argument to the `input()` function, like `input('Enter your name: ')`. That way, the user knows what to do!
To recap, remember that 'Input = I' to capture data from users, and 'Output = P' for printing results. Any questions before we move on?
Differences between Python 2 and 3
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Now, let's focus on the differences between Python 2 and 3 regarding print functions. Who remembers how print works in Python 2?
In Python 2, you can just write `print x, y` without parentheses.
Correct! That's a big difference. And how does that change in Python 3?
In Python 3, it needs parentheses, like `print(x, y)`.
Exactly! Python 3 enforces function syntax. This ensures clarity about what you're calling. Now, can anyone explain why this is important?
It helps avoid errors in code and makes it more readable for everyone!
Absolutely! Making code clear and standardized is crucial for good programming practices. Just remember, in Python 3, 'P' for print equals parentheses!
Does that mean we can’t use anything without parentheses in Python 3?
That’s correct! Using parentheses is part of defining how Python has evolved to ensure consistency across its use. Let's summarize: In Python 2, print allows flexible syntax, while in Python 3, the function call format is mandatory. Any questions?
User Input Handling in Python
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Now, let's talk about how user input is handled. In Python 2, what function do we use?
We use `raw_input()` in Python 2.
Good! And in Python 3?
We just use `input()`!
That's right! In Python 3, `input()` reads input as a string directly. Why must we keep this in mind?
Because everything is stored as a string, so we need to convert it if we want to use it as a number!
Exactly! You need to use functions like `int()` to change string inputs into numbers. Remember, 'convert to use'! Any questions?
What happens if you enter something that can't be converted?
Great question! If the input is invalid for conversion, you'll get a ValueError. We can learn to handle that using try-except blocks later. Let’s recap: Python 2 uses `raw_input()`, while Python 3 uses `input()`. Next, we also need to convert inputs when necessary.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
The section highlights the primary distinctions between Python 2 and Python 3, notably how print statements and data input via the input function differ in syntax and enforcement between these two versions. It emphasizes the necessity for explicit syntax in Python 3 compared to the more permissive format of Python 2.
Detailed
Detailed Summary
In this section, we explore the critical differences between Python 2 and 3, particularly regarding input and output functionalities. Python 2 allows for optional parentheses in the print statement, making it more flexible; e.g., print x, y would work without parentheses, while Python 3 requires a function call format: print(x, y).
Additionally, the handling of user input differs significantly: Python 2 uses raw_input() to collect input as a string, while Python 3 simplifies this to a single input() function, which reads everything as a string. Understanding these differences is vital for transitioning code between these versions and ensuring compatibility.
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Print Function Differences
Chapter 1 of 2
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Chapter Content
In python 2, you can say print space and then, give the, what is given as the arguments to print in python 3. Python 3 insists on it being called like a function, with brackets; in python 2 the brackets are optional. So, you will very often see, in python 2 code, something that looks like print x, y, given without any brackets. This is legal in python 2; this is not legal in python 3. Just be careful about this.
Detailed Explanation
In Python 2, the 'print' statement does not require parentheses, meaning you can write print x, y directly. However, in Python 3, 'print' is treated as a function and requires parentheses, so you must write it as print(x, y). This is an important difference to remember because running Python 2 style print in Python 3 will result in a syntax error.
Examples & Analogies
Think of it like a restaurant menu. In the past, you could order your food by just saying what you want, like 'burger and fries'. Now, the restaurant has updated its system, and you must fill out a form with your order enclosed in a proper box, like - 'Order: {burger and fries}'. If you don’t follow the new rules, you won’t be able to place your order.
Control Over Print Behavior
Chapter 2 of 2
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Chapter Content
And what we saw is that, with the limited amount of control, we can make print behave as we want. So, we can specify what to put at the end. In particular, we can tell it not to put a new line. So, continue printing in the same line and we can separate the values by something other than the default space character.
Detailed Explanation
In Python 3, the print function allows you to customize its behavior using 'end' and 'sep' parameters. The 'end' parameter specifies what to print at the end of the statement; by default, it's a new line. If you set 'end' to a space, it will continue printing on the same line. The 'sep' parameter allows you to determine how the values are separated when printed; by default, values are separated by a space but can be set to another character or removed entirely.
Examples & Analogies
Imagine typing a message to a friend. If you want to make sure your sentences flow together without any pauses, you would choose to write continuously instead of hitting 'enter' between each thought. Similarly, in coding, adjusting the 'end' parameter allows your output to flow without line breaks when desired.
Key Concepts
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Key Difference in Print Syntax: Python 2 allows print without parentheses; Python 3 requires them.
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User Input Handling: In Python 2, input is captured using
raw_input(), whereas in Python 3,input()is used.
Examples & Applications
In Python 2, you can write: print 'Hello, world!' vs. in Python 3, you must write: print('Hello, world!').
For input, in Python 2: name = raw_input('Enter your name: ') while in Python 3: name = input('Enter your name: ').
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
In Python 2, print is quite free, with no parentheses, just let it be!
Stories
Once upon a time, two Python siblings lived, one easy-going (Python 2) and one strict (Python 3). The strict one needed permission (parentheses) for every statement, while the easy-going sibling let you be free as a bird!
Memory Tools
P.I. (Print and Input) - remember Python 2 has print that flies free without the parentheses, while Python 3 is strict with parentheses.
Acronyms
P2PP3 (Python 2 Prints Plain, Python 3 Requires Printer Parameters); use P's for print statements!
Flash Cards
Glossary
- Python 2
An older version of Python that allows more flexible syntax for print statements and requires using
raw_input()for input.
- Python 3
The latest version of Python that enforces function syntax for print statements and uses
input()to capture user input.
- Print function
A built-in function in Python that outputs data to the screen.
- Input function
A built-in function in Python that reads a line of input from the user.
Reference links
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