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Python

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2.5. Indenting Code

2.5. Indenting Code

Python functions have no explicit begin or end, and no curly braces to mark where the function code starts and stops. The only delimiter is a colon (:) and the indentation of the code itself.

Example 2.5. Indenting the buildConnectionString Function


def buildConnectionString(params):
    """Build a connection string from a dictionary of parameters.

    Returns string."""
    return ";".join(["%s=%s" % (k, v) for k, v in params.items()])

Code blocks are defined by their indentation. By "code block", I mean functions, if statements, for loops, while loops, and so forth. Indenting starts a block and unindenting ends it. There are no explicit braces, brackets, or keywords. This means that whitespace is significant, and must be consistent. In this example, the function code (including the doc string) is indented four spaces. It doesn't need to be four spaces, it just needs to be consistent. The first line that is not indented is outside the function.

Example 2.6, “if Statements” shows an example of code indentation with if statements.

Example 2.6. if Statements


def fib(n):                   1
    print 'n =', n            2
    if n > 1:                 3
        return n * fib(n - 1)
    else:                     4
        print 'end of the line'
        return 1
1 This is a function named fib that takes one argument, n. All the code within the function is indented.
2 Printing to the screen is very easy in Python, just use print. print statements can take any data type, including strings, integers, and other native types like dictionaries and lists that you'll learn about in the next chapter. You can even mix and match to print several things on one line by using a comma-separated list of values. Each value is printed on the same line, separated by spaces (the commas don't print). So when fib is called with 5, this will print "n = 5".
3 if statements are a type of code block. If the if expression evaluates to true, the indented block is executed, otherwise it falls to the else block.
4 Of course if and else blocks can contain multiple lines, as long as they are all indented the same amount. This else block has two lines of code in it. There is no other special syntax for multi-line code blocks. Just indent and get on with your life.

After some initial protests and several snide analogies to Fortran, you will make peace with this and start seeing its benefits. One major benefit is that all Python programs look similar, since indentation is a language requirement and not a matter of style. This makes it easier to read and understand other people's Python code.

Note
Python uses carriage returns to separate statements and a colon and indentation to separate code blocks. C++ and Java use semicolons to separate statements and curly braces to separate code blocks.

Further Reading on Code Indentation

Contacter le responsable de la rubrique Python

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