Coding for Humanities Python

Transcription

1 Coding for Humanities Python Gertjan van Noord October 1, 2018

2 Overview Python is a programming language Simple programs Elements of Python programs Iteration

3 Python High-level programming language Readable for humans Guido van Rossum: Benevolent Dictator For Life

4 Python: original motivation Easy and intuitive language, just as powerful as major competitors Open Source Code that is understandable as plain English Suitable for many tasks, allowing for short development times

5 The first program: hello world

6 The first program: hello world # This program displays some text on the screen def main (): print (" Hello world.") print (" Your ad here.") main ()

7 What does it take to run the program Type the lines above in a file, for instance hello.py (Note: if you use cut and paste of the lecture notes, beware that the pdf has slightly different characters for quotes and such) You can use any text editor (not word processor). For instance: gedit, sublime,... (it helps if you use an editor that knows about Python syntax) In a command interpreter, you can then type: python3 hello.py

8 Try it: Use a text editor to create the file hello.py Run it: python3 hello.py If that works, try the programs on the next sheets

9 Polite.py # A simple program that welcomes students to their first # programming course. def main (): first_name = input (" Enter your first name : ") last_name = input (" Enter your last name : ") full_name = first_name + " " + last_name main () print (" Welcome to the world of programming,", full_name + ".")

10 Average.py # This program calculates the average of two scores, # and prints the result to the screen. def main (): score1_str = input (" Enter first score : ") score2_str = input (" Enter second score : ") main () score1 = int ( score1_str ) score2 = int ( score2_str ) average = ( score1 + score2 ) / 2 print (" The average is:", average )

11 Try it yourself! Average of three numbers

12 Looking inside Python programs comments: anything on the line after # strings: anything between quotes... or... numbers: 2 functions main(), print(), input(), int() definitions introduced by keyword def variables first name, score1, score2, average assignments = operations +

13 Interactive Python $ python3 Python (default, Nov , 17:05:23) [GCC ] on linux Type "help", "copyright", "credits" or "license" for more information. >>>

14 Interactive Python $ python3 Python (default, Nov , 17:05:23) [GCC ] on linux Type "help", "copyright", "credits" or "license" for more information. >>> my_var = 3 >>> print(my_var) 3

15 Interactive Python $ python3 Python (default, Nov , 17:05:23) [GCC ] on linux Type "help", "copyright", "credits" or "license" for more information. >>> my_var = 3 >>> print(my_var) 3 >>> my_var 3 >>> my_var = my_var + 4 >>> my_var 7

16 >>> var = " this is some text " >>> var this is some text >>> var = " new text " >>> var new text Numbers and Strings

17 Numbers and Strings >>> var = 3 >>> newvar = var + 1 Traceback ( most recent call last ): File "<stdin >", line 1, in <module > TypeError : Can t convert int object to str implicitly >>> int ( var ) 3 >>> newvar = int ( var ) + 1 >>> newvar 4

18 >>> for i in range (10):... print (i,i*i) >>> Iteration

19 >>> for i in range (2,10):... print (i,i*i) Iteration

20 >>> sum =0 >>> for i in range (10):... sum = sum +i... >>> sum Iteration

21 >>> sum =0 >>> for i in range (10):... sum = sum +i... >>> sum 45 Iteration

22 Exercise Write a program that prints the sum of the squares of the numbers 0 up to 100

23 ...

24 My solution # A program which prints the sum of the squares of the integers def main (): sum =0 for i in range (100): sum = sum +i*i print ( sum ) main ()

25 Much shorter solution! # A program which prints the sum of the squares of the integers def main (): print (328350) main ()

26 Computational Problem A computational problem requires some notion of input (an instance of the problem) The output (the solution) depends on the input

27 Exercise Write a program that prints the sum of the squares of the numbers 0 up to N, where N is the number the user of the program types in as input to the program

28 My solution # A program which prints the sum of the squares of the integers # 0.. N where N is input by the user def main (): upto = input ( Please type a number : ) sum =0 for i in range ( int ( upto )): sum = sum +i*i print ( sum ) main () $ python3 nsquares.py Please type a number:

29 Iteration over lines of input # This program adds line numbers to the lines of its input. import sys def main (): nr = 1 for line in sys. stdin : line = line. rstrip () # remove newline character print (nr, "\t", line ) nr = nr + 1 main ()

30 By typing lines of input on the keyboard How can we use this?

31 How can we use this? By typing lines of input on the keyboard Programs we build can be part of a pipe too! For example (first cp/download tweets.txt): cat tweets.txt python3 num.py 1 digbickbicycle i deadass thot she was gonna death drop 2 AlisonKayEY 5 principles of #DigitalAcceleration: 5) Digital is cultural shift - #banks need to get better at #collabora 3 katiebmarketing The link between #diversity #fakenews and the capacity of your organisation to deal with #disruption + # 4 Stupidcounter one million five hundred eighteen thousand six hundred seventy four 5 technetes It will be disaster if these #talktalk routers used for #DDOS, they need to relase new #firm 6 mickaebooks its all over my ice popsicle and pretend that it is raining 7 Barcelona all the way 8 What microphone are you using in your Facebook videos? Are those shot on a phone or a video 9 SoryahhTale Our #Xmas #StorytellingCafe is very nearly upon us! Next Monday 12 Dec with GRAHAM LANGLEY & 10 EngelhardtZ Beatrice - tul az operencian.mp4

32 But first... Resources for the course: can be copied from /net/shared/vannoord/coding/ if you are on a LWP machine otherwise, can be downloaded from Coding/Resources

33 Exercises Write a program sum.py that reads lines which should consist of a single number. After all lines have been read, the program prints the sum of all numbers. First test your program interactively. If you think it works, try this: (after cp/download numbers.txt): cat numbers.txt python3 sum.py 165 As the previous exercise, but now the program should also print the average of all numbers. Call this program average.py. cat numbers.txt python3 average.py The function len(var) will return the length of a given string. Use this function to write a program length.py that copies each line, but adds the line length in front of each line.

34 cat lot.txt python3 length.py head Cathy zag hen wild zwaaien. 88 Haar vader stak zijn duim omhoog alsof hij wilde zeggen : " het komt Write a program charcount.py that prints the total number of characters of the input cat lot.txt python3 charcount.py 1445 Write a program average length.py that prints the average line length of the input. cat lot.txt python3 average_length.py