Python Syntax : The Python language has many similarities to Perl, C, and Java. However, there are some definite differences between the languages.
First Python Program
Let us execute programs in different modes of programming.
Interactive Mode Programming
Invoking the interpreter without passing a script file as a parameter brings up the following prompt −
Python 2.4.3 (#1, Nov 11 2010, 13:34:43)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-48)] on linux2
Type “help”, “copyright”, “credits” or “license” for more information.
Type the following text at the Python prompt and press the Enter −
>>> print "Hello, Python!"
If you are running new version of Python, then you would need to use print statement with parenthesis as in print (“Hello, Python!”);. However in Python version 2.4.3, this produces the following result −
Script Mode Programming
Invoking the interpreter with a script parameter begins execution of the script and continues until the script is finished. When the script is finished, the interpreter is no longer active.
Let us write a simple Python program in a script. Python files have extension .py. Type the following source code in a test.py file −
print "Hello, Python!"
We assume that you have Python interpreter set in PATH variable. Now, try to run this program as follows −
$ python test.py
This produces the following result −
A Python identifier is a name used to identify a variable, function, class, module or other object. An identifier starts with a letter A to Z or a to z or an underscore (_) followed by zero or more letters, underscores and digits (0 to 9).
Python does not allow punctuation characters such as @, $, and % within identifiers. Python is a case sensitive programming language. Thus, Manpower and manpower are two different identifiers in Python.
Here are naming conventions for Python identifiers −
- Class names start with an uppercase letter. All other identifiers start with a lowercase letter.
- Starting an identifier with a single leading underscore indicates that the identifier is private.
- Starting an identifier with two leading underscores indicates a strongly private identifier.
- If the identifier also ends with two trailing underscores, the identifier is a language-defined special name.
The following list shows the Python Syntax keywords. These are reserved words and you cannot use them as constant or variable or any other identifier names. All the Python keywords contain lowercase letters only.