Execute Python SyntaxAs we learned in the previous page, Python syntax can be executed by writing directly in the Command Line: Show
>>> print("Hello, World!") Or by creating a python file on the server, using the .py file extension, and running it in the Command Line: C:\Users\Your Name>python myfile.py Python IndentationIndentation refers to the spaces at the beginning of a code line. Where in other programming languages the indentation in code is for readability only, the indentation in Python is very important. Python uses indentation to indicate a block of code. Python will give you an error if you skip the indentation: The number of spaces is up to you as a programmer, the most common use is four, but it has to be at least one. Example if 5 > 2: Try it Yourself » You have to use the same number of spaces in the same block of code, otherwise Python will give you an error: ExampleSyntax Error: if 5 > 2: Try it Yourself » Python VariablesIn Python, variables are created when you assign a value to it: Python has no command for declaring a variable. You will learn more about variables in the Python Variables chapter. CommentsPython has commenting capability for the purpose of in-code documentation. Comments start with a #, and Python will render the rest of the line as a comment: ExampleComments in Python: #This is a comment. Try it Yourself » Test Yourself With ExercisesExercise:Insert the missing part of the code below to output "Hello World". Start the Exercise The Python language has many similarities to Perl, C, and Java. However, there are some definite differences between the languages. First Python ProgramLet us execute programs in different modes of programming. Interactive Mode ProgrammingInvoking the interpreter without passing a script file as a parameter brings up the following prompt − $ python 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 − Hello, Python! Script Mode ProgrammingInvoking 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 − Hello, Python! Let us try another way to execute a Python script. Here is the modified test.py file − #!/usr/bin/python print "Hello, Python!" We assume that you have Python interpreter available in /usr/bin directory. Now, try to run this program as follows − $ chmod +x test.py # This is to make file executable $./test.py This produces the following result − Hello, Python! Python IdentifiersA 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 −
Reserved WordsThe following list shows the Python 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.
Lines and IndentationPython provides no braces to indicate blocks of code for class and function definitions or flow control. Blocks of code are denoted by line indentation, which is rigidly enforced. The number of spaces in the indentation is variable, but all statements within the block must be indented the same amount. For example − if True: print "True" else: print "False" However, the following block generates an error − if True: print "Answer" print "True" else: print "Answer" print "False" Thus, in Python all the continuous lines indented with same number of spaces would form a block. The following example has various statement blocks − Note − Do not try to understand the logic at this point of time. Just make sure you understood various blocks even if they are without braces. #!/usr/bin/python import sys try: # open file stream file = open(file_name, "w") except IOError: print "There was an error writing to", file_name sys.exit() print "Enter '", file_finish, print "' When finished" while file_text != file_finish: file_text = raw_input("Enter text: ") if file_text == file_finish: # close the file file.close break file.write(file_text) file.write("\n") file.close() file_name = raw_input("Enter filename: ") if len(file_name) == 0: print "Next time please enter something" sys.exit() try: file = open(file_name, "r") except IOError: print "There was an error reading file" sys.exit() file_text = file.read() file.close() print file_text Multi-Line StatementsStatements in Python typically end with a new line. Python does, however, allow the use of the line continuation character (\) to denote that the line should continue. For example − total = item_one + \ item_two + \ item_three Statements contained within the [], {}, or () brackets do not need to use the line continuation character. For example − days = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday'] Quotation in PythonPython accepts single ('), double (") and triple (''' or """) quotes to denote string literals, as long as the same type of quote starts and ends the string. The triple quotes are used to span the string across multiple lines. For example, all the following are legal − word = 'word' sentence = "This is a sentence." paragraph = """This is a paragraph. It is made up of multiple lines and sentences.""" Comments in PythonA hash sign (#) that is not inside a string literal begins a comment. All characters after the # and up to the end of the physical line are part of the comment and the Python interpreter ignores them. #!/usr/bin/python # First comment print "Hello, Python!" # second comment This produces the following result − Hello, Python! You can type a comment on the same line after a statement or expression − name = "Madisetti" # This is again comment You can comment multiple lines as follows − # This is a comment. # This is a comment, too. # This is a comment, too. # I said that already. Following triple-quoted string is also ignored by Python interpreter and can be used as a multiline comments: ''' This is a multiline comment. ''' Using Blank LinesA line containing only whitespace, possibly with a comment, is known as a blank line and Python totally ignores it. In an interactive interpreter session, you must enter an empty physical line to terminate a multiline statement. Waiting for the UserThe following line of the program displays the prompt, the statement saying “Press the enter key to exit”, and waits for the user to take action − #!/usr/bin/python raw_input("\n\nPress the enter key to exit.") Here, "\n\n" is used to create two new lines before displaying the actual line. Once the user presses the key, the program ends. This is a nice trick to keep a console window open until the user is done with an application. Multiple Statements on a Single LineThe semicolon ( ; ) allows multiple statements on the single line given that neither statement starts a new code block. Here is a sample snip using the semicolon − import sys; x = 'foo'; sys.stdout.write(x + '\n') Multiple Statement Groups as SuitesA group of individual statements, which make a single code block are called suites in Python. Compound or complex statements, such as if, while, def, and class require a header line and a suite. Header lines begin the statement (with the keyword) and terminate with a colon ( : ) and are followed by one or more lines which make up the suite. For example − if expression : suite elif expression : suite else : suite Command Line ArgumentsMany programs can be run to provide you with some basic information about how they should be run. Python enables you to do this with -h − $ python -h usage: python [option] ... [-c cmd | -m mod | file | -] [arg] ... Options and arguments (and corresponding environment variables): -c cmd : program passed in as string (terminates option list) -d : debug output from parser (also PYTHONDEBUG=x) -E : ignore environment variables (such as PYTHONPATH) -h : print this help message and exit [ etc. ] You can also program your script in such a way that it should accept various options. Command Line Arguments is an advanced topic and should be studied a bit later once you have gone through rest of the Python concepts. How do you write syntax in Python?Execute Python Syntax
As we learned in the previous page, Python syntax can be executed by writing directly in the Command Line: >>> print("Hello, World!") Hello, World!
How do I start my Python code?The Easiest Way to Run Python. Download Thonny IDE.. Run the installer to install Thonny on your computer.. Go to: File > New. Then save the file with . py extension. ... . Write Python code in the file and save it. Running Python using Thonny IDE.. Then Go to Run > Run current script or simply click F5 to run it.. What is the syntax of Python language?The syntax of the Python programming language is the set of rules which defines how a Python program will be written. Python Line Structure: A Python program is divided into a number of logical lines and every logical line is terminated by the token NEWLINE. A logical line is created from one or more physical lines.
Does Python have a syntax?The syntax of the Python programming language is the set of rules that defines how a Python program will be written and interpreted (by both the runtime system and by human readers). The Python language has many similarities to Perl, C, and Java.
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