Review Day 2¶
- Give an example of a tuple
- What is the difference between a tuple and a list?
- How would you approach a complicated coding task?
- What is the different syntax between a function and a method?
- Calculate the average of the list [1,2,3.5,5,6.2] to one decimal
- Take the list ['i','know','python'] as input and output the string 'I KNOW PYTHON'
Tuples¶
Give an example of a tuple:
In [3]:
myTuple = (1,2,3,'a','b',[4,5,6])
myTuple
Out[3]:
What is the difference between a tuple and a list?
A tuple is immutable while a list is mutable
How to structure code¶
- Decide on what output you want
- What input files do you have?
- How is the input structured, can you iterate over it?
- Where is the information you need located?
- Do you need to save a lot of information while iterating?
- Lists are good for ordered data
- Sets are good for non-duplicate single entry information
- Dictionaries are good for a lot of structured information
- When you have collected the data needed, decide on how to process it
- Are you writing your results to a file?
Always start with writing pseudocode!
Functions and methods¶
What is the different syntax between a function and a method?
functionName() <object>.methodName()
Calculate the average of the list [1,2,3.5,5,6.2] to one decimal
In [4]:
myList = [1,2,3,5,6]
round(sum(myList)/len(myList),1)
Out[4]:
Take the list ['i','know','python'] as input and output the string 'I KNOW PYTHON'
In [5]:
' '.join(['i','know','python']).upper()
Out[5]:
Day 3¶
- Sets
- Dictionaries
- Functions
- sys.argv
In [1]:
fh = open('../downloads/250.imdb', 'r', encoding = 'utf-8')
genres = []
for line in fh:
if not line.startswith('#'):
cols = line.strip().split('|')
genre = cols[5].strip()
glist = genre.split(',')
for entry in glist:
if entry.lower() not in genres: # only add genre if not already in list
genres.append(entry.lower())
fh.close()
print(genres)
print(len(genres))
New data type: set¶
- A set contains an unordered collection of unique and immutable objects
Syntax:
For empty set:
setName = set()
For populated sets:
setName = {1,2,3,4,5}
Common operations on sets¶
set.add(a)
len(set)
a in set
In [7]:
x = set()
x.add(100)
x.add(25)
x.add(3)
x.add('3.0')
#for i in x:
# print(type(i))
type(x)
##mySet = {2,5,1,3}
#mySet.add(5)
#mySet.add(4)
#print(mySet)
Out[7]:
In [9]:
fh = open('../downloads/250.imdb', 'r', encoding = 'utf-8')
genres = set()
for line in fh:
if not line.startswith('#'):
cols = line.strip().split('|')
genre = cols[5].strip()
glist = genre.split(',')
for entry in glist:
genres.add(entry.lower()) # set only adds entry if not already in
fh.close()
print(len(genres))
sorted(list(genres))
Out[9]:
... Hm, starting to be difficult now...
New data type: dictionary¶
- A dictionary is a mapping of unique keys to values
- Dictionaries are mutable
Syntax:
a = {} (create empty dictionary)
d = {'key1':1, 'key2':2, 'key3':3}
In [10]:
myDict = {'drama': 4,
'thriller': 2,
'romance': 5}
myDict
Out[10]:
Operations on Dictionaries¶
In [11]:
myDict = {'drama': 4,
'thriller': 2,
'romance': 5}
len(myDict)
myDict['drama']
myDict['horror'] = 2
#myDict
#del myDict['horror']
#myDict
'drama' in myDict
myDict.keys()
myDict.items()
myDict.values()
Out[11]:
Exercise¶
In [ ]:
myDict = {'drama': 182,
'war': 30,
'adventure': 55,
'comedy': 46,
'family': 24,
'animation': 17,
'biography': 25}
- How many entries are there in this dictionary?
- How do you find out how many movies are in the genre 'comedy'?
- You're not interested in biographies, delete this entry
- You are however interested in fantasy, add that we have 29 movies of the genre fantasy to the list
- What genres are listed in this dictionary?
- You remembered another comedy movie, increase the number of comedies by one
In [ ]:
Find the number of movies per genre¶
Hint! If the genre is not already in the dictionary, you have to add it first
Answer¶
In [ ]:
fh = open('../downloads/250.imdb', 'r', encoding = 'utf-8')
genreDict = {} # create empty dictionary
for line in fh:
if not line.startswith('#'):
cols = line.strip().split('|')
genre = cols[5].strip()
glist = genre.split(',')
for entry in glist:
if not entry.lower() in genreDict: # check if genre is not in dictionary, add 1
genreDict[entry.lower()] = 1
else:
genreDict[entry.lower()] += 1 # if genre is in dictionary, increase count with 1
fh.close()
print(genreDict)
What is the average length of the movies (hours and minutes) in each genre?¶
In [ ]:
fh = open('../downloads/250.imdb', 'r', encoding = 'utf-8')
genreDict = {}
for line in fh:
if not line.startswith('#'):
cols = line.strip().split('|')
genre = cols[5].strip()
glist = genre.split(',')
runtime = cols[3] # length of movie in seconds
for entry in glist:
if not entry.lower() in genreDict:
genreDict[entry.lower()] = [int(runtime)] # add a list with the runtime
else:
genreDict[entry.lower()].append(int(runtime)) # append runtime to existing list
fh.close()
for genre in genreDict: # loop over the genres in the dictionaries
average = sum(genreDict[genre])/len(genreDict[genre]) # calculate average length per genre
hours = int(average/3600) # format seconds to hours
minutes = (average - (3600*hours))/60 # format seconds to minutes
print('The average length for movies in genre '+genre\
+' is '+str(hours)+'h'+str(round(minutes))+'min')
NEW TOPIC: Functions¶
A lot of ugly formatting for calculating hours and minutes from seconds...
In [12]:
def FormatSec(genre): # input a list of seconds
average = sum(genreDict[genre])/len(genreDict[genre])
hours = int(average/3600)
minutes = (average - (3600*hours))/60
return str(hours)+'h'+str(round(minutes))+'min'
fh = open('../downloads/250.imdb', 'r', encoding = 'utf-8')
genreDict = {}
for line in fh:
if not line.startswith('#'):
cols = line.strip().split('|')
genre = cols[5].strip()
glist = genre.split(',')
runtime = cols[3] # length of movie in seconds
for entry in glist:
if not entry.lower() in genreDict:
genreDict[entry.lower()] = [int(runtime)] # add a list with the runtime
else:
genreDict[entry.lower()].append(int(runtime)) # append runtime to existing list
fh.close()
for genre in genreDict:
print('The average length for movies in genre '+genre\
+' is '+FormatSec(genre))
Function structure¶
Function structure¶
In [13]:
def addFive(number):
final = number + 5
return final
addFive(4)
Out[13]:
In [14]:
from datetime import datetime
def whatTimeIsIt():
time = 'The time is: ' + str(datetime.now().time())
return time
whatTimeIsIt()
Out[14]:
In [15]:
def addFive(number):
final = number + 5
return final
addFive(4)
#final
final = addFive(4)
final
Out[15]:
Scope¶
- Variables within functions
- Global variables
In [16]:
def someFunction():
# s = 'a string'
print(s)
s = 'another string'
someFunction()
print(s)
Why use functions?¶
- Cleaner code
- Better defined tasks in code
- Re-usability
- Better structure
Importing functions¶
- Collect all your functions in another file
- Keeps main code cleaner
- Easy to use across different code
Example:
- Create a file called myFunctions.py, located in the same folder as your script
- Put a function called
formatSec()in the file - Start writing your code in a separate file and
importthe function
In [17]:
from myFunctions import formatSec
seconds = 32154
formatSec(seconds)
Out[17]:
In [18]:
from myFunctions import formatSec, toSec
seconds = 21154
print(formatSec(seconds))
days = 0
hours = 21
minutes = 56
seconds = 45
print(toSec(days, hours, minutes, seconds))
myFunctions.py¶
Summary¶
- A function is a block of organized, reusable code that is used to perform a single, related action
- Variables within a function are local variables
- Functions can be organized in separate files and imported to the main code
→ Notebook Day_3_Exercise_1 (~30 minutes)
NEW TOPIC AGAIN: sys.argv¶
- Avoid hardcoding the filename in the code
- Easier to re-use code for different input files
- Uses command-line arguments
- Input is list of strings:
- Position 0: the program name
- Position 1: the first argument
The `sys.argv` function
Python script called print_argv.py:
Running the script with command line arguments as input:
Instead of:
do:
Run with:
IMDb¶
Re-structure and write the output to a new file as below
Note:
- Use a text editor, not notebooks for this
- Use functions as much as possible
- Use
sys.argvfor input/output
