Dictionary

# inizializzo con curl brakets
d = {'Norway':'Oslo','Sweden':'Sockholm','France':'Paris'}
# aggiungo un elemento
d['Germany'] = 'Berlin'
print(d['Germany'])

# inizializzo con dict
temps = dict(Oslo='13',London=15.4,Paris=17.5)
for citta, temperatura in sorted(temps.items()):
    print(f"La temperatura media a {citta} è {temperatura}°C")

# cerco se una determinata chiave esiste
if 'Berlin' in temps:
    print('Berlin:', temps['Berlin'])
else:
    print('No temperature data for Berlin')

# cancello uno degli elementi
del temps['Oslo']
print(temps)

# per accedere a chiave e valore separatamente
# temps.keys() --- temps.values()
for temp in temps.values():
    print(temp)
# posso copiare
t2 = temps.copy()

Berlin
La temperatura media a London è 15.4°C
La temperatura media a Oslo è 13°C
La temperatura media a Paris è 17.5°C
No temperature data for Berlin
{'London': 15.4, 'Paris': 17.5}
15.4
17.5

A Dictionary of Polynomials

$$\large p(x) = -1+x^2+3x^7$$

poly = {0:-1,2:1,7:3}
x = 1
def eval_poly_dict(poly, x):  
    sum = 0.0  
    for power in poly:  
        sum += poly[power]*x**power 
    return sum
print(eval_poly_dict(poly, x))

3.0

poly = {0:-1,2:1,7:3}
x = 1
def eval_poly_dict(poly, x):  
    #Python’s sum can add elements of an iterator  
    return sum(poly[power]*x**power for power in poly)
print(eval_poly_dict(poly, x))

3

Posso fare anche partendo da una List

p = [-1,0,1,0,0,0,0,3]
x = 1
def eval_poly_list(poly, x):  
    sum = 0  
    for power in range(len(poly)):  
        sum += poly[power]*x**power  
    return sum
print(eval_poly_list(p, x))    

3

Posso fare ache mediante Enumerate

Qui dobbiamo memorizzare tutti gli zeri

p = [-1,0,1,0,0,0,0,3]
x = 1
def eval_poly_list_enum(poly, x):  
    sum = 0
    # power, coeff sono due tuple
    for power, coeff in enumerate(poly):  
        sum += coeff*x**power  
    return sum
print(eval_poly_list(p, x))

3

Se vogliamo un sistema "sparse"

p = {0:-1,2:1,7:3}  
def eval_poly_dict(poly, x):  
    #Python’s sum can add elements of an iterator  
    return sum(poly[power]*x**power for power in poly)
print(eval_poly_dict(p, x=1))

3

Reading File Data to a Dictionary

# creo un dizionario vuoto, poi riempio
with open('deg2.txt','r') as infile:
    temps = {}
    for line in infile:
        city, temp = line.split()
        city = city[:-1]
        temps[city] = float(temp)
print(temps)

{'Oslo': 21.8, 'London': 18.1, 'Berlin': 19.0, 'Paris': 23.0, 'Rome': 26.0, 'Helsinki': 17.8}

Strings

s = 'Berlin: 18.4 C at 4 pm'
for s_ in s:
    print(s_,end=' ')
    
print('')
print(s.find('Berlin'))
print(s.find('pm'))
print(s.find('Oslo'))

print('Berlin' in s)

s.replace('Berlin','Bonn')

B e r l i n :   1 8 . 4   C   a t   4   p m 
0
20
-1
True

'Bonn: 18.4 C at 4 pm'

Splitting and Joining Strings

s = 'Berlin: 18.4 C at 4 pm'
print(s.split(':'))
print(s.split())

['Berlin', ' 18.4 C at 4 pm']
['Berlin:', '18.4', 'C', 'at', '4', 'pm']

strings = ['Newton', 'Secant','Biscection']
print(', '.join(strings))

Newton, Secant, Biscection

"""
Tromso Norway 69.6351 18.9920 52436
Molde Norway 62.7483 7.1833 18594
Oslo Norway 59.9167 10.7500 835000
Stockholm Sweden 59.3508 18.0973 1264000
Uppsala Sweden 59.8601 17.6400 133117
"""
cities = {}  
with open('cities.txt') as infile:  
    for line in infile:  
        words = line.split()  
        name = ', '.join(words[:2])  
        data = {'lat': float(words[2]), 'long':float(words[3])}  
        data['pop'] = int(words[4])  
        cities[name] = data
print(cities)

{'Tromso, Norway': {'lat': 69.6351, 'long': 18.992, 'pop': 52436}, 'Molde, Norway': {'lat': 62.7483, 'long': 7.1833, 'pop': 18594}, 'Oslo, Norway': {'lat': 59.9167, 'long': 10.75, 'pop': 835000}, 'Stockholm, Sweden': {'lat': 59.3508, 'long': 18.0973, 'pop': 1264000}, 'Uppsala, Sweden': {'lat': 59.8601, 'long': 17.64, 'pop': 133117}}

String Manupulation

t = '1st line\r\n2nd line\r\n3rd line' #Windows
print(t)
t = '1st line\n2nd line\n3rd line' #Mac, Unix format
print(t.splitlines())
t = '1st line\r\n2nd line\r\n3rd line' #Windows
print(t.splitlines()) #cross platform!

1st line
2nd line
3rd line
['1st line', '2nd line', '3rd line']
['1st line', '2nd line', '3rd line']

String are constant, immutable objects !

Posso aggiungere pezzi o procedere con replace()

s = '    text with leading/trailibg spaces    '
print('"'+s.strip()+'"')
print('"'+s.lstrip()+'"')
print('"'+s.rstrip()+'"')

"text with leading/trailibg spaces"
"text with leading/trailibg spaces    "
"    text with leading/trailibg spaces"

s = 'Berlin: 18.4 C at 4 pm'
print(s.startswith('Berlin'))
print(s.endswith('am'))
print(s.lower())
print(s.upper())

True
False
berlin: 18.4 c at 4 pm
BERLIN: 18.4 C AT 4 PM

Reading a pair of numbers from a file

pairs = [] 
#list of (n1, n2) pairs of numbers  
with open('pairs.txt', 'r') as lines:  
    for line in lines:  
        words = line.split()  
        for word in words:  
            word = word[1:-1] #strip off parentheses
            #print(word)
            n1, n2 = word.split(',')  
            n1 = float(n1); n2 = float(n2)  
            pair = (n1, n2)  
            pairs.append(pair) 
print(pairs)

[(1.3, 0.0), (-1.0, 2.0), (3.0, -1.5), (0.0, 1.0), (1.0, 0.0), (1.0, 1.0), (0.0, -0.01), (10.5, -1.0), (2.5, -2.5)]