Boston Python workshop 2/Friday tutorial: Difference between revisions
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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. |
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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In this case, because <code>1</code> is truthy, Python executes the code block under the if statement, and we see "I'm True!" printed to the screen. What do you think will happen |
In this case, because <code>1</code> is truthy, Python executes the code block under the if statement, and we see "I'm True!" printed to the screen. What do you think will happen with this one: |
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<pre> |
<pre> |
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if "": |
if "": |
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print "empty strings are truthy" |
print "empty strings are truthy" |
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</pre> |
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You can use the <code>else</code> keyword to conditionally execute code when the expression for the <code>if</code> block isn't true: |
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<pre> |
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sister_age = 15 |
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brother_age = 12 |
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if sister_age > brother_age: |
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print "Sister is older" |
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else: |
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print "brother is older" |
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</pre> |
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You can check multiple expressions together using the <code>and</code> and <code>or</code> keywords. If two expressions are joined by an <code>and</code>, they <b>both</b> have to be True for the overall expression to be True. If two expressions are joined by an <code>or</code>, as long as <b>one</b> is True, the overall expression to be True. |
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<pre> |
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1 > 0 and 1 < 2 |
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</pre> |
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<pre> |
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1 < 2 and "x" in "abc" |
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</pre> |
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<pre> |
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"a" in "hello" or "e" in hello" |
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</pre> |
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<pre> |
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1 < 0 or "x" in "abc" |
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</pre> |
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<pre> |
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hour = 11 |
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if hour < 7 or hour > 23: |
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print "Go away!" |
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print "I'm sleeping!" |
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else: |
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print "Welcome to the cheese shop!" |
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print "Can I interest you in some choice gouda?" |
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</pre> |
</pre> |
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