Core Python Programming (2nd Edition)

3.1.3. Multiple Statement Groups as Suites ( : )
Groups of individual statements making up a single code block are called "suites" in Python (as we
introduced in Chapter 2). Compound or complex statements, such as if, while, def, and class, are
those that require a header line and a suite. Header lines begin the statement (with the keyword) and
terminate with a colon ( tt ) and are followed by one or more lines that make up the suite. We will refer
to the combination of a header line and a suite as a clause.
3.1.4. Suites Delimited via Indentation
As we introduced in Section 2.10, Python employs indentation as a means of delimiting blocks of code.
Code at inner levels are indented via spaces or tabs. Indentation requires exact indentation; in other
words, all the lines of code in a suite must be indented at the exact same level (e.g., same number of
spaces). Indented lines starting at different positions or column numbers are not allowed; each line
would be considered part of another suite and would more than likely result in syntax errors.
Core Style: Indent with four spaces and avoid using tabs
As someone who is perhaps new to block delimitation using
whitespace, a first obvious question might be: How many spaces
should I use? We think that two is too short, and six to eight is too
many, so we suggest four spaces for everyone. Also, because tabs
vary in the number of spaces depending on your system, we
recommend not using tabs if there is any hint of cross-platform
development. Both of these style guidelines are also supported by
Guido van Rossum, the creator of Python, and documented in the
Python Style Guide. You will find the same suggestions in our style
guide in Section 3.4.
A new code block is recognized when the amount of indentation has increased, an d its termination is
signaled by a "dedentation," or a reduction of indentation matching a previous level's. Code that is not
indented, i.e., the highest level of code, is considered the "main" portion of the script.
The decision to create code blocks in Python using indentation was based on the belief that grouping
code in this manner is more elegant and contributes to the ease of reading to which we alluded earlier.
It also helps avoid "dangling-else"-type problems, including ungrouped single statement clauses (those
where a C if statement does not use braces at all, but has two indented statements following). The
second statement will execute regardless of the conditional, leading to more programmer confusion until
the light bulb finally blinks on.
Finally, no "holy brace wars" can occur when using indentation. In C (also C++ and Java), starting
braces may be placed on the same line as the header statement, or may start the very next line, or may
be indented on the next line. Some like it one way, some prefer the other, etc. You get the picture.
3.1.5. Multiple Statements on a Single Line ( ; )
The semicolon ( ; ) allows multiple statements on a 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')