Boston Python Workshop 4/ColorWall handout: Difference between revisions
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That's way more clever than I was expcetnig. Thanks! |
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===ColorWall goals=== |
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* practice for loops |
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* practice using functions |
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* practice implementing functions |
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* have fun experimenting with Python code that produces graphical results |
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===Concept review=== |
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====Indentation reminder==== |
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In Python, indentation matters. Everything is indented by a multiple |
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of some number of spaces, often 4. |
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In <code>if</code> statements, you indent everything you want to be run if the if |
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conditional is <code>True</code>. For example: |
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<pre> |
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>>> James = 35 |
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>>> Alice = 30 |
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>>> if James > Alice: |
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... print "James is older than Alice." |
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... |
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James is older than Alice. |
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>>></pre> |
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Because James really is older than Alice, the <code>if</code> conditional is <code>True</code>, |
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so Python does execute the code indented under the if line. In this |
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case we print "James is older than Alice." |
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<pre> |
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>>> James = 35 |
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>>> Alice = 30 |
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>>> if James < Alice: |
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... print "James is younger than Alice." |
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... |
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>>></pre> |
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Because James is not older than Alice, the <code>if</code> conditional is <code>False</code>, so |
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Python does not execute the code indented under the if line. |
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In for loops, you indent everything you want to be run each loop For |
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example: |
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<pre> |
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>>> names = ["Jessica", "Adam", "Liz"] |
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>>> for name in names: |
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... print "Hello", name |
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... |
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Hello Jessica |
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Hello Adam |
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Hello Liz</pre> |
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The <code>print</code> line is indented 4 spaces under the <code>for</code>. That's how |
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Python knows to execute the print line for every name in names. |
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====dictionaries==== |
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* dictionaries are a way to map keys to values |
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* if you used a Python dictionary to store the information from a real dictionary, the keys would be words and the values would be definitions |
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* dictionaries aren't ordered (lists are ordered) |
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<pre> |
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>>> flavors = {"Jessica" : "Chocolate", "Adam" : "Vanilla", "Liz" : "Strawberry"} |
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>>> flavors["Jessica"] |
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'Chocolate' |
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>>> flavors["Eve"] |
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Traceback (most recent call last): |
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File "<stdin>", line 1, in <module> |
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KeyError: 'Eve' |
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>>> flavors.get("Eve") |
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>>> flavors["Eve"] = "Rocky Road" |
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>>> flavors |
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{'Eve': 'Rocky Road', 'Jessica': 'Chocolate', 'Liz': 'Strawberry', 'Adam': 'Vanilla'}</pre> |
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====getting keys and values from dictionaries==== |
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* use keys() to get a list of keys |
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* use values() to get a list of values |
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<pre> |
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>>> flavors = {"Jessica" : "Chocolate", "Adam" : "Vanilla", "Liz" : "Strawberry"} |
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>>> for person in flavors.keys(): |
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... print person |
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... |
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Jessica |
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Liz |
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Adam |
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>>> for flavor in flavors.values(): |
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... print flavor |
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... |
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Chocolate |
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Strawberry |
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Vanilla</pre> |
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====range==== |
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<pre> |
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>>> range(5) |
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[0, 1, 2, 3, 4] |
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>>> for i in range(5): |
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... print "Hi" * i |
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... |
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Hi |
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HiHi |
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HiHiHi |
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HiHiHiHi</pre> |
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====<code>if</code> statements inside <code>for</code> loops==== |
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<pre> |
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>>> for i in range(80): |
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... if i % 9 == 0: |
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... print i, "is divisible by 9." |
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... |
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0 is divisible by 9. |
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9 is divisible by 9. |
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18 is divisible by 9. |
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27 is divisible by 9. |
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36 is divisible by 9. |
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45 is divisible by 9. |
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54 is divisible by 9. |
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63 is divisible by 9. |
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72 is divisible by 9.</pre> |
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====<code>for</code> loops inside <code>for</code> loops==== |
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<pre> |
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>>> letters = ["a", "b", "c"] |
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>>> numbers = [1, 2, 3] |
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>>> for letter in letters: |
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... for number in numbers: |
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... print letter * number |
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... |
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a |
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aa |
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aaa |
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b |
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bb |
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bbb |
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c |
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cc |
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ccc |
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>>> for number in numbers: |
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... for letter in letters: |
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... print number * letter |
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... |
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a |
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b |
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c |
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aa |
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bb |
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cc |
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aaa |
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bbb |
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ccc</pre> |
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====Imports==== |
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Imports look like this: |
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<pre> |
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>>> import random |
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>>> import time</pre> |
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In the above example, <code>random</code> and <code>time</code> are both Python modules. Modules |
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are Python files outside of the current Python file that contain |
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Python code, like functions and variables. You can use code from |
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modules by first importing the module. Here's an example from the |
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<code>random</code> module: |
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<pre> |
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>>> import random |
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>>> random.randint(0, 10) |
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7 |
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>>> random.randint(0, 10) |
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6 |
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>>> random.randint(0, 10) |
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1 |
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>>> random.randint(0, 10) |
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3 |
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>>> random.randint(0, 10) |
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4 |
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>>> random.randint(0, 10) |
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9</pre> |
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<code>randint</code> is a function in the <code>random</code> module. It takes a lower bound as |
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the first argument and an upper bound as the second argument and |
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returns a random integer between those bounds. |
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Revision as of 15:54, 15 January 2012
That's way more clever than I was expcetnig. Thanks!