Lecture notes 3#
Numbers#
Example: suppose you have a recepe which requires “red” milk, and you only have “green” milk, how much milk do you have to replace with cream to get the same fat content. With required volume \(v\) and replaced volume \(x\) we have a fat-balance equation
\[1.5\% (v - x) + 40 \% x = 3\% v\]
\[x = \frac{3 - 1.5}{40 - 1.5}v \]
v = 1
x = (3 - 1.5)/(40-1.5) * v
print(x)
0.03896103896103896
For a litre, in tablespoon units, replace about 40ml (~2.5 table spoons)
With some refactoring, introduce more variable names
required_volume = 1
required_fat_content = 3 # in percent
available_fat_content = 1.5
cream_fat_content = 40
replaced_volume = (required_fat_content - available_fat_content)/(cream_fat_content-available_fat_content) * required_volume
print(replaced_volume)
0.03896103896103896
one line got a bit too long, introduce another intermediate variable conversion_ratio
required_volume = 1
required_fat_content = 3 # in percent
available_fat_content = 1.5
cream_fat_content = 40
conversion_ratio = (required_fat_content - available_fat_content)/(cream_fat_content-available_fat_content)
replaced_volume = conversion_ratio * required_volume
print(replaced_volume)
0.03896103896103896
Strings#
"It's time"
"It's time"
# 'It's time' invalid
Cell In[7], line 1
'It's time'
^
SyntaxError: unterminated string literal (detected at line 1)
'It\'s time' # \' means use the literal character '
"It's time"
print("""
Hello
world
""")
Hello
world
"""
Hello
world
"""
'\nHello\nworld\n'
\n means newline character
'hello' + 'world'
'helloworld'
'bye' + 'bye'
'byebye'
'bye' + 'bye' + 'bye'
'byebyebye'
with this definition of addition a generalized integer multiplication follows
3 * 'bye'
'byebyebye'
Some string functions (or methods)
'gone with the wind'.capitalize()
'Gone with the wind'
'gone with the wind'.title()
'Gone With The Wind'
Suppose we want to underline a title such that
Gone With The Wind
==================
movie = 'gone with the wind'
movie.title() + "\n" + "="*len(movie)
'Gone With The Wind\n=================='
print(movie.title() + "\n" + "="*len(movie))
Gone With The Wind
==================
Lists#
colours = ['hearts', 'spades', 'diamonds', 'clubs']
colours[0]
'hearts'
colours[3]
'clubs'
colours[4]
---------------------------------------------------------------------------
IndexError Traceback (most recent call last)
Cell In[20], line 1
----> 1 colours[4]
IndexError: list index out of range
len(colours)
4
# the last element
colours[len(colours) - 1]
'clubs'
colours[-1] # counts from the end
'clubs'
colours[-2]
'diamonds'
colours
['hearts', 'spades', 'diamonds', 'clubs']
colours[-1] = 'CLUBS'
colours
['hearts', 'spades', 'diamonds', 'CLUBS']
colours_tuple = ('hearts', 'spades', 'diamonds', 'clubs')
colours_tuple[0]
'hearts'
colours_tuple[-1]
'clubs'
colours_tuple[-1] = 'CLUBS'
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
Cell In[36], line 1
----> 1 colours_tuple[-1] = 'CLUBS'
TypeError: 'tuple' object does not support item assignment
dictionaries#
newdict = {'a': 1, 'b': 2}
len(newdict)
2
newdict.keys()
dict_keys(['a', 'b'])
newdict.values()
dict_values([1, 2])
newdict['a']
1
newdict['b']
2
evaluate#
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