Therefore, it's common to have the boilerplate if _name_ =. When a Python file is run directly, the special variable "_name_" is set to "_main_". A Python module can be run directly - as above "python hello.py Bob" - or it can be imported and used by some other module. The outermost statements in a Python file, or "module", do its one-time setup - those statements run from top to bottom the first time the module is imported somewhere, setting up its variables and functions. Imports, Command-line arguments, and len()
hello.py Alice # without needing 'python' first (Unix) Running this program from the command line looks like: # Standard boilerplate to call the main() function to begin # sys.argv is the script name itself and can be ignored # Command line args are in sys.argv, sys.argv. # import modules used here - sys is a very standard one
#Python code code
Here's a very simple hello.py program (notice that blocks of code are delimited strictly using indentation rather than curly braces - more on this later!): See the official docs page on all the different options you have when running Python from the command-line. Python source files use the ".py" extension and are called "modules." With a Python module hello.py, the easiest way to run it is with the shell command "python hello.py Alice" which calls the Python interpreter to execute the code in hello.py, passing it the command line argument "Alice". Comments begin with a '#' and extend to the end of the line. The end of a line marks the end of a statement, so unlike C++ and Java, Python does not require a semicolon at the end of each statement. Like C++ and Java, Python is case sensitive so "a" and "A" are different variables. Also, the interpreter throws, or "raises" in Python parlance, a runtime error if the code tries to read a variable that has not been assigned a value. "Python 3.", these examples should work for you.Īs you can see above, it's easy to experiment with variables and operators. The version of python you're using and where it was built. The two lines python prints after you type python and before the > prompt tells you about > ^D # type CTRL-d to exit (CTRL-z in Windows/DOS terminal) > foo # try something else that doesn't work > a + str(len(a)) # probably what you really wanted TypeError: can only concatenate str (not "int") to str > a + len(a) # try something that doesn't work > len(a) # call the len() function on a string > a = 'hi' # 'a' can hold a string just as well > a # entering an expression prints its value > a = 6 # set a variable in this interpreter session Type "help", "copyright", "credits" or "license" for more information. Python 3.X.X (XXX, XXX XX XXXX, 03:41:42) on XXX If you ever have a question like, "What happens if I add an int to a list?" Just typing it into the Python interpreter is a fast and likely the best way to see what happens. Python tracks the types of all values at runtime and flags code that does not make sense as it runs.Īn excellent way to see how Python code works is to run the Python interpreter and type code right into it. This makes the code short and flexible, and you lose the compile-time type checking of the source code. There are no type declarations of variables, parameters, functions, or methods in source code. Python is a dynamic, interpreted (bytecode-compiled) language. What's this "interpreter" we mention? You'll find out in the next section! Language Introduction
Finally, if you're seeking self-paced online learning without watching videos, try the ones listed towards the end of this post - each feature learning content as well as a Python interactive interpreter you can practice with. If you're seeking a companion MOOC course, try the ones from Udacity and Coursera ( intro to programming or intro to Python). As mentioned on the setup page, this material covers Python 3. It is based on the introductory Python course offered internally. Welcome to Google's Python online tutorial.
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