07. Functions

Exercise 1

def is_prime(x):
    for j in range(2, x):
        if x % j == 0:
            return False
    return True

is_prime(7)

True

Exercise 2

With loop

def factorial(x):
    fact = 1
    for i in range(1,x+1):
        fact = fact * i
    return fact

Without loop

def factorial(x):
    if x > 0:
        return x * factorial(x - 1)
    else:
        return 1

Exercise 3

def mean(x):
    return sum(x) / float(len(x))

mean([1, 3, 4, 5, 6, 7])

4.333333333333333

08. Reading and writing files

Exercise 1

# Open file
f = open('data/data.txt', 'r')

# Read and ignore header lines
header1 = f.readline()
header2 = f.readline()
header3 = f.readline()

jmag = {}
for line in f:
    line = line.strip()
    columns = line.split()
    name = columns[2]
    jmag[name] = float(columns[3])

jmag

{'00424403+4116069': 9.321,
 '00424403+4116108': 11.507,
 '00424433+4116085': 9.453,
 '00424446+4116016': 12.07,
 '00424455+4116103': 10.773,
 '00424464+4116092': 9.299,
 '00424464+4116106': 9.399}

for name in sorted(jmag):  # alphabetical
    print(name, jmag[name])

00424403+4116069 9.321
00424403+4116108 11.507
00424433+4116085 9.453
00424446+4116016 12.07
00424455+4116103 10.773
00424464+4116092 9.299
00424464+4116106 9.399

Exercise 2

# Open file
f_in = open('data/data.txt', 'r')
f_out = open('data_new.txt', 'w')

# Read and ignore header lines
header1 = f_in.readline()
header2 = f_in.readline()
header3 = f_in.readline()

# Loop over lines and extract variables of interest
for line in f_in:
    line = line.strip()
    columns = line.split()
    name = columns[2]
    jmag = float(columns[3])
    f_out.write(name + " " + str(jmag) + "\n")

f_out.close()

%cat data_new.txt

00424433+4116085 9.453
00424403+4116069 9.321
00424455+4116103 10.773
00424464+4116092 9.299
00424403+4116108 11.507
00424464+4116106 9.399
00424446+4116016 12.07

09. Modules and Variable Scope

import math

math.cos(math.radians(60))

0.5000000000000001

math.sin(math.pi / 6)

0.49999999999999994