#!/usr/bin/env python
# coding: utf-8
# Introduction to Python (2)
# ===
# Sequence types
# ===
#
# Lists
# ---
#
# Mutable sequences of values.
# In[1]:
l = [2, 5, 2, 3, 7]
type(l)
# Lists can be heterogeneous, but we typically don't use that.
# In[2]:
a = 'spezi'
[3, 'abc', 1.3e20, [a, a, 2]]
# Sequence types
# ===
#
# Tuples
# ---
#
# Immutable sequences of values.
# In[3]:
t = 'white', 77, 1.5
type(t)
# In[4]:
color, width, scale = t
width
# Sequence types
# ===
#
# Strings (1/2)
# ---
#
# Immutable sequences of characters.
# In[5]:
'a string can be written in single quotes'
# Strings can also be written with double quotes, or over multiple lines with triple-quotes.
# In[6]:
"this makes it easier to use the ' character"
# In[7]:
"""This is a multiline string.
You see? I continued after a blank line."""
# Sequence types
# ===
#
# Strings (2/2)
# ---
#
# A common operation is formatting strings using argument substitutions.
# In[8]:
'{} times {} equals {:.2f}'.format('pi', 2, 6.283185307179586)
# Accessing arguments by position or name is more readable.
# In[9]:
'{1} times {0} equals {2:.2f}'.format('pi', 2, 6.283185307179586)
# In[10]:
'{number} times {amount} equals {result:.2f}'.format(number='pi', amount=2,
result=6.283185307179586)
# Sequence types
# ===
#
# Common operations (1/2)
# ---
#
# All sequence types support concatenation, membership/substring tests, indexing, and slicing.
# In[11]:
[1, 2, 3] + [4, 5, 6]
# In[12]:
'bier' in 'we drinken bier vanaf half 5'
# In[13]:
'abcdefghijkl'[5]
# Sequence types
# ===
#
# Slicing
# ---
#
# Slice `s` from `i` to `j` with `s[i:j]`.
# In[14]:
'abcdefghijkl'[4:8]
# In[15]:
'abcdefghijkl'[:3]
# We can also define the step `k` with `s[i:j:k]`.
# In[16]:
'abcdefghijkl'[7:3:-1]
# Sequence types
# ===
#
# Common operations (2/2)
# ---
#
# Contrary to strings and tuples, lists are mutable. We can also get their length, smallest/largest item, and number/position of certain items.
# In[17]:
len('attacgataggcatccgt')
# In[18]:
max([17, 86, 34, 51])
# In[19]:
('atg', 22, True, 'atg').count('atg')
# Sequence types
# ===
#
# Additional operations with lists
# ---
#
# We can replace, add, remove, reverse and sort items in-place.
# In[20]:
l = [1, 2, 3, 4]
l[3] = 7
l.append(1)
l[1:3] = [3, 2]
l.sort()
l.reverse()
# In[21]:
l
# Dictionaries
# ===
#
# Dictionaries map *hashable* values to arbitrary objects
# ---
#
# * All built-in immutable objects are hashable.
# * No built-in mutable objects are hashable.
# In[22]:
d = {'a': 27, 'b': 18, 'c': 12}
type(d)
# In[23]:
d['e'] = 17
'e' in d
# In[24]:
d.update({'a': 18, 'f': 2})
d
# Dictionaries
# ===
#
# Accessing dictionary content
# ---
# In[25]:
d['b']
# In[26]:
d.keys()
# In[27]:
d.values()
# In[28]:
d.items()
# Sets
# ===
#
# Mutable unordered collections of hashable values without duplication
# ---
# In[29]:
x = {12, 28, 21, 17}
type(x)
# In[30]:
x.add(12)
x
# In[31]:
x.discard(21)
x
# Sets
# ===
#
# Operations with sets
# ---
#
# We can test for membership and apply many common set operations such as union and intersect.
# In[32]:
17 in {12, 28, 21, 17}
# In[33]:
{12, 28, 21, 17} | {12, 18, 11}
# In[34]:
{12, 28, 21, 17} & {12, 18, 11}
# Booleans
# ===
#
# Boolean values and operations
# ---
#
# The two boolean values are written `False` and `True`.
# In[35]:
True or False
# In[36]:
True and False
# In[37]:
not False
# Booleans
# ===
#
# Comparisons
# ---
#
# Comparisons can be done on all objects and return a boolean value.
# In[38]:
22 * 3 > 66
# We have two equivalence relations: value equality (`==`) and object identity (`is`).
# In[39]:
a, b = [1, 2, 3], [1, 2, 3]
a == b
# In[40]:
a is b
# Booleans
# ===
#
# `if` statements
# ---
#
# (The `print` statement writes a string representation of the given value.)
# In[41]:
if 26 <= 17:
print 'Fact: 26 is less than or equal to 17'
elif (26 + 8 > 14) == True:
print 'Did we need the ` == True` part here?'
else:
print 'Nothing seems true'
# Booleans
# ===
#
# `while` statements
# ---
#
# Our first looping control structure just repeats until the given expression evaluates to `False`.
# In[42]:
i = 0
while i < 5:
print i
i += 1
# Hands on!
# ===
#
# Try to guess the outcome of the following statements:
#
# 2 * 3 > 4
# 2 * (3 > 4)
# 2 * (4 > 3)
# Notes about syntax
# ===
#
# Indentation
# ---
#
# Python uses indentation to delimit blocks
#
# * Instead of `begin ... end` or `{ ... }` in other languages.
# * Always increase indentation by *4 spaces*, never use tabs.
# * In any case, be consistent.
# In[43]:
if False:
if False:
print 'Why am I here?'
else:
while True:
print 'When will it stop?'
print "And we're back to the first indentation level"
# Some editors can be configured to behave just like that.
# Notes about syntax
# ===
#
# Comments
# ---
#
# Comments are prepended by `#` and completely ignored.
# In[44]:
# Add 42 to this list.
l.append(42)
# `pass` statements
# ---
#
# If you ever need a statement syntactically but don't want to do anything, use `pass`.
# In[45]:
while False:
# This is never executed anyway.
pass
# Useful built-ins
# ===
#
# Getting help
# ---
#
# You can get help on almost any object with `help`.
# In[46]:
help(range)
# In IPython you can do it faster by typing:
# In[47]:
get_ipython().run_line_magic('pinfo', 'range')
# Useful built-ins
# ===
#
# We'll shortly use the following built-in functions.
# In[48]:
range(5, 16)
# In[49]:
zip(['red', 'white', 'blue'], range(3))
# In[50]:
list('abcdefghijk')
# Iteration
# ===
#
# Iterating over a sequence
# ---
# In[51]:
colors = ['red', 'white', 'blue', 'orange']
cities = ['leiden', 'utrecht', 'warmond', 'san francisco']
# The `for` statement can iterate over sequence items.
# In[52]:
for color in colors:
print color
# In[53]:
for character in 'blue':
print character
# Iteration
# ===
#
# Python anti-patterns
# ---
#
# These are common for programmers coming from other languages.
# In[54]:
i = 0
while i < len(colors):
print colors[i]
i += 1
# In[55]:
for i in range(len(colors)):
print colors[i]
# We call them *unpythonic*.
# Iteration
# ===
#
# Using values *and* indices
# ---
# In[56]:
for i, color in enumerate(colors):
print i, '->', color
# Taking two sequences together
# ---
# In[57]:
for city, color in zip(cities, colors):
print city, '->', color
# Iteration
# ===
#
# Other iterables
# ---
#
# Iterating over a dictionary yields keys.
# In[58]:
for key in {'a': 33, 'b': 17, 'c': 18}:
print key
# Iterating over a file yields lines.
# In[59]:
for line in open('data/short_file.txt'):
print line
# There are many more useful iterables in Python.
#
#
Hands on!
#
#
# - Make a list with 10 integer elements. Sum all the items in the list.
# - Make a new list from the above one that does not include the 0th, 4th and 5th elements.
#
- Sum only the elements from the first list which are between the 2nd and 6th elements.
#
- Make a new list that includes only the elements that are greater than 10 from the first list.
#
- Food.
#
# - Create a dictionary for food products called "prices" and put some values in it, e.g., "apples": 2, "oranges": 1.5, "pears": 3, ...
# - Create a corresponding dictionary called "stocks" and put the stock values in it, e.g., "apples": 0, "oranges": 1, "pears": 10, ...
# - Print stock and price information for each food item.
# - Determine and print how much money you would make if you sold all of your food products.
#
#
#
#
#