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Boston Python workshop 2/Friday tutorial: Difference between revisions
Boston Python workshop 2/Friday tutorial (view source)
Revision as of 00:01, 27 May 2011
, 13 years ago→Flow Control
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==Flow Control==
We can use these expressions that <i>evaluate</i> to booleans to make decisions:
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print "1 is truthy"
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That was our first multi-line piece of code, and the way to enter it at a Python prompt is a little different. First, type the <code>if 1:</code> part, and hit enter. The next line will have <code>...</code> as a prompt, instead of the usual <code>>>></code>. This is Python telling us that we are in the middle of a <b>code block</b>, and so long as we indent our code it should be a part of this code block.
Type 4 spaces, and then type <code>print "1 is truthy"</code>. Hit enter to end the line, and hit enter again to tell Python you are done with this code block. All together, it will look something like this:
<pre>
>>> if 1:
... print "1 is truthy"
...
1 is truthy
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So what is going on here? When Python encounters the <code>if</code> keyword, it <i>evaluates</i> the <i>expression</i> following the keyword and before the colon. If that expression is <b>True</b>, Python executes the code in the indented code block under the <code>if</code> line. If that expression is <b>False</b>, Python skips over the code block:
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