Python

Question 1

change a tuple

Answer 1

illegal

Question 2

add element to list

Answer 2

a.append(elem)

Question 3

add two lists

Answer 3

a + [1, 3]

Question 4

get last list element

Answer 4

a[-1]

Question 5

copy index 1, 2 and 3 to sublist

Answer 5

a[1:4]

Question 6

delete element with a given index

Answer 6

del a[i]

Question 7

remove an element with a given value

Answer 7

a.remove(value)

Question 8

find index corresponding to an element’s value

Answer 8

a.index(value)

Question 9

test if a value is contained in the list

Answer 9

value in a

Question 10

count how many elements that have given value

Answer 10

a.count(value)

Question 11

number of elements in list a

Answer 11

len(a)

Question 12

the smallest element in a

Answer 12

min(a)

Question 13

the largest element in a

Answer 13

max(a)

Question 14

add all elements in a

Answer 14

sum(a)

Question 15

sort list

Answer 15

a.sort() # changes a

Question 16

sort list into a new list

Answer 16

sorted(a)

Question 17

reverse list

Answer 17

a.reverse() # changes a

Question 18

check if a is a list

Answer 18

isinstance(a, list)

Question 19

Print full names

names = ["Ola", "Per", "Kari"]
surnames = ["Olsen", "Pettersen", "Bremnes"]

Answer 19

for name, surname in zip(names, surnames):

print name, surname

Question 20

Print indexes and names

names = [“Ola”, “Per”, “Kari”]

Answer 20

for i, name in enumerate(names):

print i, name

Question 21

evaluate string expressions

Answer 21

r = eval(‘x + 2.2’)

Question 22

read a file

Answer 22

file = open(filename, ‘r’)
for line in file:
print line
infile.close()

Question 23

write to file

Answer 23

file = open(filename, ‘w’) # or ‘a’ to append
file.write(“””
….
“””)

Question 24

initialize a dictionary

Answer 24

a = {'point': [2,7], 'value': 3}
a = dict(point=[2,7], value=3)

Question 25

add new key-value pair to a dictionary

Answer 25

a[‘key’] = value

Question 26

delete a key-value pair from the dictionary

Answer 26

del a[‘key’]

Question 27

list of keys in dictionary

Answer 27

a.keys()

Question 28

list of values in dictionary

Answer 28

a.values()

Question 29

number of key-value pairs in dictionary

Answer 29

len(a)

Question 30

loop over keys in unknown order

Answer 30

for key in a:

Question 31

loop over keys in alphabetic order

Answer 31

for key in sorted(a.keys()):

Question 32

check if a is a dictionary

Answer 32

isinstance(a, dict)

Question 33

get index of char in string

Answer 33

str.find(‘char’)

Question 34

split string into substrings

Answer 34

str.split(‘:’)

Question 35

test if substring is in string

Answer 35

substring in string

Question 36

remove leading/trailing blanks

Answer 36

str.strip()

Question 37

combine list into string with delimiter

Answer 37

’, ‘.join(list)

Question 38

file blogging

Answer 38

import glob

files = glob.glob(‘*.pdf’)

Question 39

check for directory

Answer 39

import os.path

os.path.isdir(myfile)

Question 40

get file size

Answer 40

import stat

os.stat(myfile)[stat.ST_SIZE]

Question 41

copy a file

Answer 41

import shutil

shutil.copy(myfile, newfile)

Question 42

rename a file

Answer 42

import os

os.rename(myfile, ‘newname’)

Question 43

remove a file

Answer 43

import os

os.remove(‘filename’)

Question 44

create directory

Answer 44

os.mkdir(dirname)

Question 45

create path out of strings

Answer 45

os.path.join(os.environ[‘HOME’], ‘py’, ‘src’)

Question 46

remove directory

Answer 46

shutil.rmtree(‘myroot’)

Question 47

get filename out of full path

Answer 47

os.path.basename(path)

Question 48

traverse directory

Answer 48

def myfunc(arg, dirname, files):
   for filename in files:
       arg.append(filename)
os.path.walk(os.environ['HOME'], myfunc, list)
for filename in list:
    print filename

Question 49

print with variables

Answer 49

print ‘%d: %s’ % (index, string)

Question 50

a = [1, 2]
b = a
a is b?

Answer 50

True

Question 51

make a copy of list

Answer 51

b = a[:]

Question 52

make a copy of dictionary

Answer 52

b = a.copy()

Question 53

run stand-alone application

Answer 53

from subprocess import Popen, PIPE
p = Popen(cmd, shell=True, stdout=PIPE)
output, errors = p.communicate()

Question 54

read file into a list of lines

Answer 54

file = open(filename, 'r')
lines = file.readlines()

Question 55

convert string to float

Answer 55

float(str)

Question 56

boolean type

Answer 56

bool a = True

Question 57

convert all elements in list to float

Answer 57

y = map(float, y)

Question 58

define comparison criterion

Answer 58

def comparator(s1, s2):
    # return -1, 0, 1
list.sort(comparator)

Question 59

replace in string

Answer 59

str.replace(this, withThis)

Question 60

multi-line string

Answer 60

str = “””
…
“””

Question 61

substring fra string

Answer 61

string[1:5]

Question 62

Are string mutable?

Answer 62

No, strings (and tuples) are immutable

Question 63

change global variables inside function

Answer 63

global varName

Question 64

main-function

Answer 64

if __name__ == ‘__main__’:

Question 65

doc string

Answer 65

first string in functions, classes, files

Question 66

print doc string

Answer 66

> > > print function.__doc__

Question 67

doctest

Answer 67

Inside doc string:
"""
>>> function(3)
6.0
"""

import doctest
doctest.testmod(function)

Question 68

run doctest

Answer 68

Just run the script!

import doctest
doctest.testmod(function)

Question 69

define class w/ constructor

Answer 69

class MyClass(object):
    conter = 0 # static variable
    def \_\_init\_\_(self, i): # constructor
        self.i = i;

Question 70

create object of class

Answer 70

obj = MyClass(5)

Question 71

define subclass

Answer 71

class SubClass(MyClass):
    def \_\_init\_\_(self, i, j):
        MyClass.\_\_init\_\_(self, i)
        self.j = j

Question 72

public, protected, private

Answer 72

a = # public
_b = # non-public
\_\_c = # private

Question 73

class instance: dictionary of user-defined attributes

Answer 73

instance.__dict__

Question 74

class name from instance

Answer 74

instance.__class__.__name__

Question 75

list names of all methods and attributes in class instance

Answer 75

dir(instance)

Question 76

difference between is and ==

Answer 76

is checks object identity

== checks for equal contents

Question 77

when is a evaluated as true?

Answer 77

if a has
__len__ or
__nonzero__
and the return value is 0 or False

Question 78

list of local variables

list of global variables

Answer 78

locals()

global()

Question 79

simple timer

Answer 79

import timeit

print timeit.timeit(function, number=100)

Question 80

profiler

Answer 80

import profile

profile = profile.run(“func()”)

Question 81

save profiling data to file, read afterwards

Answer 81

import profile
profile = profile.run(“func()”, “result.txt”)

import pstats
data = pstats.Stats(“result.txt”)
data.print_stats()