BDACA - Lecture2

You are encouraged to start up
a Python environment (like
Spyder or Jupyter Notebook). If
you do so, you can try out the
examples while listening. If you prefer
to listen only, that’s ﬁne as well.

Basics Exercise Next meetings
Big Data and Automated Content Analysis
Week 2 – Monday
»Getting started with Python«
Damian Trilling
d.c.trilling@uva.nl
@damian0604
www.damiantrilling.net
Afdeling Communicatiewetenschap
Universiteit van Amsterdam
12 February 2018
Big Data and Automated Content Analysis Damian Trilling

Today
1 The very, very, basics of programming with Python
Datatypes
Functions and methods
Modifying lists and dictionaries
Indention: The Python way of structuring your program
2 Exercise
3 Next meetings

The very, very, basics of programming
See also Chapter 4.

Datatypes
Python lingo
Basic datatypes (variables)
int 32
ﬂoat 1.75
bool True, False
string "Damian"

Datatypes
Python lingo
int 32
float 1.75
bool True, False
string "Damian"
(variable name firstname)
"firstname" and firstname is not the same.

Datatypes
Python lingo
int 32
float 1.75
bool True, False
string "Damian"
(variable name firstname)
"firstname" and firstname is not the same.
"5" and 5 is not the same.
But you can transform it: int("5") will return 5.
You cannot calculate 3 * "5" (In fact, you can. It’s "555").
But you can calculate 3 * int("5")

Datatypes
Python lingo
More advanced datatypes
Note that the elements of a list, the keys of a dict, and the values
of a dict can have any datatype! (Better to be consistent, though!)

Datatypes
Python lingo
list firstnames = [’Damian’,’Lori’,’Bjoern’]
lastnames =
[’Trilling’,’Meester’,’Burscher’]

Datatypes
Python lingo
lastnames =
list ages = [18,22,45,23]

Datatypes
Python lingo
lastnames =
list ages = [18,22,45,23]
dict familynames= {’Bjoern’: ’Burscher’,
’Damian’: ’Trilling’, ’Lori’: ’Meester’}
dict {’Bjoern’: 26, ’Damian’: 31, ’Lori’:
25}

Python lingo
Functions

Python lingo
Functions
functions Take an input and return something else
int(32.43) returns the integer 32. len("Hello")
returns the integer 5.

Python lingo
Functions
methods are similar to functions, but directly associated with
an object. "SCREAM".lower() returns the string
"scream"

Python lingo
Functions
methods are similar to functions, but directly associated with
an object. "SCREAM".lower() returns the string
"scream"
Both functions and methods end with (). Between the (),
arguments can (sometimes have to) be supplied.

Writing own functions
You can write an own function:
1 def addone(x):
2 y = x + 1
3 return y
Functions take some input (“argument”) (in this example, we
called it x) and return some result.
Thus, running
1 addone(5)
returns 6.

Modifying lists
Appending to a list
1 mijnlijst = ["element 1", "element 2"]
2 anotherone = "element 3" # note that this is a string, not a list!
3 mijnlijst.append(anotherone)
4 print(mijnlijst)
gives you:
1 ["element 1", "element 2", "element 3"]

Modifying lists
Merging two lists
1 mijnlijst = ["element 1", "element 2"]
2 anotherone = ["element 3", "element 4"]
3 mijnlist.extend(anotherone) # or simply: mijnlijst += anotherone
4 print(mijnlijst)
gives you:
1 ["element 1", "element 2", "element 3", "element 4]

Modifying dicts
Adding a key to a dict (or changing the value of an existing
key)
1 mydict = {"whatever": 42, "something": 11}
2 mydict["somethingelse"] = 76
3 print(mydict)
gives you:
1 {’whatever’: 42, ’somethingelse’: 76, ’something’: 11}
If a key already exists, its value is simply replaced.

Indention: The Python way of structuring your program

Indention
Indention
Structure
The program is structured by TABs or SPACEs

Indention
Indention
Structure
1 firstnames=[’Damian’,’Lori’,’Bjoern’]
2 age={’Bjoern’: 27, ’Damian’: 32, ’Lori’: 26}
3 print ("The names and ages of these people:")
4 for naam in firstnames:
5 print (naam,age[naam])

Indention
Indention
Structure
1 firstnames=[’Damian’,’Lori’,’Bjoern’]
2 age={’Bjoern’: 27, ’Damian’: 32, ’Lori’: 26}
3 print ("The names and ages of these people:")
Don’t mix up TABs and spaces! Both are valid, but you have
to be consequent!!! Best: always use 4 spaces!

Indention
Indention
Structure
1 print ("The names and ages of all these people:")
4 if naam=="Damian":
5 print ("He teaches this course")
6 elif naam=="Lori":
7 print ("She is a former assistant")
8 elif naam=="Bjoern":
9 print ("He helped teaching this course in the past")
10 else:
11 print ("No idea who this is")

Indention
Indention
The line before an indented block starts with a statement
indicating what should be done with the block and ends with a :

Indention
Indention
Indention of the block indicates that

Indention
Indention
• it is to be executed repeatedly (for statement) – e.g., for
each element from a list

Indention
Indention
• it is only to be executed under speciﬁc conditions (if, elif,
and else statements)

Indention
Indention
• an alternative block should be executed if an error occurs
(try and except statements)

Indention
Indention
• an alternative block should be executed if an error occurs
(try and except statements)
• a ﬁle is opened, but should be closed again after the block has
been executed (with statement)

Exercise
We’ll now together do some simple exercises . . .

Exercise
Exercises
1. Warming up
• Create a list, loop over the list, and do something with each
value (you’re free to choose).
2. Did you pass?
• Think of a way to determine for a list of grades whether they
are a pass (>5.5) or fail.
• Can you make that program robust enough to handle invalid
input (e.g., a grade as ’ewghjieh’)?
• How does your program deal with impossible grades (e.g., 12
or -3)?
• . . .

Next meetings

Wednesday
We will work together on “Describing an existing structured
dataset” (Appendix A).
Preparation: Make sure you understood all of today’s
concepts!

BDACA - Lecture2

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