Python 101 slides from Lets code group! https://www.facebook.com/letscodeblacksburg

1. Python 101
McBryde 101
Feb 22, 2013

2. Overview for Today
1. Setting up Python
2. Background on Python
3. Basics of Python
4. Data Structures in Python
5. Control Structures in Python
6. Functions in Python

3. Things you should do
Ask questions!
If you are confused, there is a 80% chance that
someone else is even more confused.
Participate!
We're all friends here. Tell us if we're going too slowly.
Tell us if we're boring. Tell us if have an idea for
something.
Follow along!
Open up Python and try stuff!

4. Setting up Python

5. Download & Install Python
http://www.python.org/download/
Run python
Windows: python.exe
Mac/Linux: python

6. Background on Python

7. What is Python?
● A language
● An interpreter
● A reference to a British sketch comedy:
"Monty Python's Flying Circus"
(The documentation is full of jokes referencing the
show)

8. Why Python?
● Traditional languages (C++, C, Java)
evolved for large-scale programming
● Scripting language (Perl, Python) evolved
for simplicity and flexibility

9. The Python Language
● Free!
● Elegant and Powerful!
● Cross-Platform!
● Tons of useful modules!
● Chock full of technical buzzwords!
○ Object-oriented, dynamic-typing

10. The "Zen" of Python
Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
...
Readability Counts
... (It's actually a lot longer)

11. The Basics

12. Printing in Python
>>> print "Hello World."
Hello World.
Meanwhile, in Java land:
public class MyFirstProgram {
public static void main(String[] args) {
System.out.println("Hello World");
}
}

13. Input in Python
>>> input("Tell me something: ")
Tell me something:
Type something in and press enter

14. Comments in Python
>>> # This is a comment
...
The following will NOT work:
/*
Multiline comment in Java
*/
// Single line comment in Java

15. Scripts in Python
1. In your IDE/Text Editor, write
# My first program!
print "Hello", "World"
2. Save the file as helloworld.py
3. From the terminal,
> python helloworld.py
Hello World.

16. Congratulations!
You are now all Python programmers.

17. Basic Data

18. Values in Python
-5 # Integer type
23.1 # Float type
"Some words" # String type
True # Boolean type
Variables in Python
age = 23
miles_from_home = 301.36
name = "Cory Bart"
has_dog = False

19. Operators
Numerics Strings
1 + 4 "Hello " + "World"
2 - 3 "Repeat" * 5
4 * 1
10.0 / 2 Comparisons
10.5 // 2 10 >= 5
2 ** 4 3 < 80
22 % 12 5 == 10
3 != 3

20. Operators continued...
Boolean logic
True and False
True or True
not True

21. Exercise
given a string myString and a
numbernumRepetitions, return myString
multiplied numRepetitions times.
multiplyString('a', 4) → 'aaaa'
multiplyString('Hello', 2) → 'HelloHello'
multiplyString('Python', 3) →
'PythonPythonPython'

22. Control and Data Structures

23. If statements
if has_dogs:
print "Has dogs"
elif age >= 25:
print "Can rent a car"
elif name == "Ellie" or name == "Becky"
print "Is awesome!"
else:
print "Not a great fellow"
*Note the white-space!*

24. Defining functions
def add(first, second):
return first + second
value = add(10, 5)

25. Exercise
Write a function that can compute tips for a
meal, given the price and how generous the
user is.
# price: float
# generous: string, either "stingy"
# or "generous"
# returns a float indicating tip
def calculate_tip(price, generosity):
...

26. Multiple returns!
def flip_coordinates(pos):
x, y = pos
return -x, -y
x, y = flip_coordinates((5, -5))

27. Sequences
Lists are Mutable and Ordered
a_list = [1, 3, 2]
Tuples are Immutable and Ordered
a_tuple = (1, 2, 3)
Sets are Mutable, Unordered, and Unique
a_set = set([1, 2, 3])
Dictionaries are Key-Value pairs
a_dictionary = {'A': 1, 'B': 2, 'C': 3}
Strings are immutable sequences of one-character Strings!
a_string = "Also a sequence!"

28. Working with a list
colors = ['red', 'blue', 'yellow', 'purple']
Add to a list
colors.append('green') or colors.insert
(index)
Remove from a list
colors.pop() or colors.remove(index)

29. Sets are a little different
>>> set([1, 1, 2, -2, 3, 3, 4])
set([1, 2, -2, 3, 4])
>>> set([1, 2, -2, 3, 4]).add(4)
set([1, 2, -2, 3, 4])
>>> set([1, 2, -2, 3, 4]).add(5)
set([1, 2, -2, 3, 4, 5])

30. Tuples are a little different
>>> my_tuple = (1, 2, 3, 4)
>>> my_tuple.add(5)
NOPE!
Tuples will be more awesome when we get to
functions.

31. Dictionaries are wonderful
>>> scores = {"Cory": 32,
"Ellie": 100,
"Becky": 78}
>>> print scores["Cory"]
32

32. Working with sequences
Get an element of a sequence:
"Puzzle"[2]
Get the length of a sequence
len(set([1, 2, 3, 4, 5, 6]))
Is something in a sequence?
5 in (1, 2, 3, 4, 5)
Get a sublist from a list
['red', 'blue', 'yellow', 'green'][1:2]
There are many built-in functions for sequences
sum((1, 2, 3, 4))
min((5, 10, 15))

33. Strings have a ton of methods!
"1, 2, 3, 4".split(",")
",".join([1,2,3,4])
" whitespace ".strip()
"I am 22".replace("am", "was")
"HeLlO wOrLd".swapcase()

34. Converting between types
str(5) -> "5"
int("10") -> 10
float("10.0") -> 10.0
bool(None) -> False
list((1, 2, 3, 4)) -> [1,2,3,4]
tuple([1, 2, 4, 8]) -> (1,2,4,8)

35. Truthiness in Python
True False
True False
5 0
-5 []
[1, 2, 3] ""
"Hello world" None
items_left = [1, 2, 3]
while items_left:
print items_left.pop()

36. Looping
The for-each loop is best!
List
for item in [1, 2, 3]: Set
print item Tuple
String
File handler
You can also use a while loop.
while True:
# do something

37. xrange
for value in xrange(5):
print value
0
1
2
3
4

38. Iterating with indices
for index, item in enumerate("ABCDE"):
print index, item
0 A
1 B
2 C
3 D
4 E

39. Iterating over Dictionary
a_dictionary = {'a':1,'b':2}
for key, value in a_dictionary.items():
print key, value

40. Exercise
Write a program that will "translate" a sentence
into Pyglatin:
"We only speak Pyglatin in Pyrome"
->
"Eway onlyay peaksay Yglatinpay inay yromeay"

41. List comprehensions
You can make a list by sticking a for loop inside!
[value*2 for value in range(10)]
[int(number) for number in "123456789"]

42. File I/O
file = open('word_lists.txt', 'r')
for line in file:
print line
file = open('numbers.txt', 'w')
for number in range(100):
file.write(number)

43. Importing
import random
random.choice(("Heads", "Tails"))
import sys
print sys.args
import math
print math.sqrt(36)

44. Command line arguments
>python file.py this is a test
Inside of file.py
import sys
print sys.args
Outputs
['this', 'is', 'a', 'test']

45. What should I do next?
The Python Challenge
http://www.pythonchallenge.com/
Online Books:
http://tinyurl.com/interactivepython

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