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Boston Python workshop 2/Friday tutorial: Difference between revisions
Boston Python workshop 2/Friday tutorial (view source)
Revision as of 01:54, 27 May 2011
, 12 years ago→Flow Control
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print (h + b) * 10
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==Part 1 Practice==
Read the following expressions, but don't execute them. Guess what the output will be. After you've made a guess, copy and paste the expressions at a Python prompt and check your guess.
1.
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total = 1.5 - 1/2 + ((-2.0/2) - (1.0/2))
print total
type(total)
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2.
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a = "quick"
b = "brown"
c = "fox jumps over the lazy dog"
print "The", a * 3, b * 3, c
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3.
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print 2.0 * 123, "2.0" * 123
print 2.0 * 123 + str(2.0) * 123
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4.
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a = "| (_| -()- -()- -()- -()- | -()- -()- -()- -()- ||\n"
b = "|_\_|_/___|__|__|__|___|__|___|__|___________________________||\n"
c = "|________________________________|__|__()_|__()_|__()__|_____||\n"
d = " ___|)_______________________________________________________\n"
e = "|_/(|,\____/_|___/_|____/_|______|___________________________||\n"
f = "|___/____________________________|___________________________||\n"
g = "| | | () | () | () | | ||\n"
h = "|__\___|.________________________|___\_|___\_|___\_|___|_____||\n"
i = "|__/|_______/|____/|_____/|______|___________________________||\n"
j = "|_____/__________________________|____\|____\|____\|_________||\n"
k = "|____/___________________________|___________________________||\n"
l = "|__/___\_._______________________|__|__|__|__|__|__|___|_____||\n"
print d + f + i + e + b + g + a + c + l + h + j + k
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==End of Part 1==
Congratulations! You've learned about and practiced math, strings, variables, data types, exceptions, tracebacks, and executing Python from the Python prompt and from a file.
Take a break, stretch, meet some neighbors, and ask the staff if you have any questions about this material.
==Python scripts==
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==Flow Control==
We can use these expressions that <i>evaluate</i> to booleans to make decisions and conditionally execute code:
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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.
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
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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:
<pre>
sister_age = 15
brother_age = 12
if sister_age > brother_age:
print "Sister is older"
else:
print "brother is older"
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Like with <code>if</code>, the code block under the <code>else</code> statement must be indented.
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 is True.
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1 > 0 and 1 < 2
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1 < 2 and "x" in "abc"
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1 <= 0 or "a" not in "abc"
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<pre>
temperature = 32
if temperature > 60 and temperature < 75:
print "It's nice and cozy in here!"
else:
print "Too extreme for me."
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<pre>
hour = 11
if hour < 7 or hour > 23:
print "Go away!"
print "I'm sleeping!"
else:
print "Welcome to the cheese shop!"
print "Can I interest you in some choice gouda?"
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