Tools: Quark's Outlines: Python Code Blocks

Quark’s Outlines: Python Code Blocks ## An Overview of Python Code Blocks ## What is a Python code block? ## Where do Python code blocks appear? ## A Historical Timeline of Python Code Blocks ## People invented structured code blocks ## People designed Python’s code block system ## Problems & Solutions with Python Code Blocks ## Problem: How do you group several lines to run together in Python? ## Problem: How do you define a block that runs once when imported in Python? ## Problem: How do you run a block from a string in Python? ## Problem: How do you run each line in the Python shell as a block in Python? ## Problem: How do you tell where a block ends in Python? ## Like, Comment, Share, and Subscribe Overview, Historical Timeline, Problems & Solutions When you write a Python program, you group statements together. This group is called a Python code block. A code block is a section of code that Python can run as one unit. It can be as short as one line or as long as a full module. You use code blocks in many places. A function body is a code block. A class definition is a code block. Each module you import is also a code block. Python reads these blocks and sets up the right space to run them. Python lets you group statements into code blocks that run together. The function body is a code block. Python runs it when you call greet(). You use code blocks in many parts of Python. Some blocks run once, like a module. Some blocks run many times, like a function. Python sees each block as its own unit, even if it lives inside another. You also write code blocks in the Python shell, in scripts, or by passing strings to eval() or exec(). Python sees each script, function, class, or command as a code block. If you type this into a shell or script, each line is part of the same code block. Where do Python’s code blocks come from? The idea of code blocks comes from early structured programming. Over time, blocks became the way to group logic and manage scope. Python kept this model but used indentation, not braces or symbols, to mark blocks. 1960 — Structured code flow in ALGOL introduced the idea of blocks with their own scope and control flow. 1972 — Braced blocks in C grouped statements using {} and used semicolons to end each line. 1991 — Indented blocks in Python 0.9.0 used colons and whitespace to group code without braces. 1994 — Interactive code blocks in Python shell treated each command as a block with its own scope. 2000 — String-based blocks added support for exec(), eval(), and input() as ways to run blocks from strings. 2010 — Function scopes improved with clear separation between local and global name spaces. 2025 — Code block rules stable and remain central to how Python runs structured code. How do you use Python code blocks the right way? Python code blocks let you group logic, run sections of code, and control how names are stored. These problems show how Python blocks behave in real scripts, shells, and function calls. You are writing a function to perform a task. You want to run a few lines together every time you call the function. You need Python to treat these lines as one block. Problem: You need a way to run several statements together. Solution: Python lets you define a code block using indentation under a def or class. Python lets you create a code block inside a function using indentation. All indented lines under def belong to the same code block. Python runs them together. You are writing a module that holds helper functions. You want it to run a small block of code the first time it is imported. This block should not run again. Problem: You want to define a code block that runs once. Solution: Python treats the module file itself as a code block. Python lets each module act as a single code block that runs when imported. When Python loads a module, it runs its code block once. Later imports skip it. You are building a tool that takes user input and runs it as Python code. You want to run full expressions or statements from strings, not just from files. Problem: You want to turn a string into a running code block. Solution: Python lets you use exec() to treat a string as a code block. Python lets you run code blocks from strings using exec(). The string is treated like its own code block. Python runs it in the current scope. You are typing commands into the Python shell. Each line you type runs by itself, but some lines must be grouped (like an if block). You want Python to know when the block ends. Problem: You want to run multi-line blocks in the shell. Solution: Python treats each top-level command or group as its own code block. Python runs each group of typed lines as its own code block. Python uses indentation to know when the block is complete before it runs it. You are reading or editing code. You want to know where a block begins and ends. You want to avoid mistakes from wrong spacing. Problem: You need to see code block boundaries clearly. Solution: Python uses colons and indentation to mark code blocks. Python uses indentation after colons to define the start of each code block. Only the indented line belongs to the show() block. The next line with no indent is outside. Did you find this helpful? Let me know by clicking the like button below. I'd love to hear your thoughts in the comments, too! If you want to see more content like this, don't forget to subscribe. Thanks for reading! Mike Vincent is an American software engineer and app developer from Los Angeles, California. More about Mike Vincent Templates let you quickly answer FAQs or store snippets for re-use. Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink. Hide child comments as well For further actions, you may consider blocking this person and/or reporting abuse COMMAND_BLOCK: def greet(name): print("Hello,", name) greet("Ada") # prints: # Hello, Ada Enter fullscreen mode Exit fullscreen mode COMMAND_BLOCK: def greet(name): print("Hello,", name) greet("Ada") # prints: # Hello, Ada COMMAND_BLOCK: def greet(name): print("Hello,", name) greet("Ada") # prints: # Hello, Ada COMMAND_BLOCK: x = 5 print(x + 2) # prints: # 7 Enter fullscreen mode Exit fullscreen mode COMMAND_BLOCK: x = 5 print(x + 2) # prints: # 7 COMMAND_BLOCK: x = 5 print(x + 2) # prints: # 7 COMMAND_BLOCK: def compute(): x = 2 y = 3 print("Result:", x + y) compute() # prints: # Result: 5 Enter fullscreen mode Exit fullscreen mode COMMAND_BLOCK: def compute(): x = 2 y = 3 print("Result:", x + y) compute() # prints: # Result: 5 COMMAND_BLOCK: def compute(): x = 2 y = 3 print("Result:", x + y) compute() # prints: # Result: 5 COMMAND_BLOCK: print("Running my_module.py") # prints: # Running my_module.py (on first import only) Enter fullscreen mode Exit fullscreen mode COMMAND_BLOCK: print("Running my_module.py") # prints: # Running my_module.py (on first import only) COMMAND_BLOCK: print("Running my_module.py") # prints: # Running my_module.py (on first import only) COMMAND_BLOCK: code = "x = 7\nprint('x is', x)" exec(code) # prints: # x is 7 Enter fullscreen mode Exit fullscreen mode COMMAND_BLOCK: code = "x = 7\nprint('x is', x)" exec(code) # prints: # x is 7 COMMAND_BLOCK: code = "x = 7\nprint('x is', x)" exec(code) # prints: # x is 7 COMMAND_BLOCK: x = 4 if x > 2: print("Big") # prints: # Big Enter fullscreen mode Exit fullscreen mode COMMAND_BLOCK: x = 4 if x > 2: print("Big") # prints: # Big COMMAND_BLOCK: x = 4 if x > 2: print("Big") # prints: # Big COMMAND_BLOCK: def show(): print("Inside block") print("Outside block") show() # prints: # Inside block # Outside block Enter fullscreen mode Exit fullscreen mode COMMAND_BLOCK: def show(): print("Inside block") print("Outside block") show() # prints: # Inside block # Outside block COMMAND_BLOCK: def show(): print("Inside block") print("Outside block") show() # prints: # Inside block # Outside block