06.01
def is_prime(x):
is_prime=True
for j in range(2,x):
if (x%j==0):
is_prime=False
break
return is_prime
is_prime(43)
06.02
# here the multiplication is done explicitly
#
# note for x<0 it also returns 1
#
def factorial_loop(x):
ans=1
for i in range(1,x+1):
ans*=i
return ans
print(factorial_loop(5))
# using recursive function calls
#
# factorial_recursive stops once the returned value is 1
#
def factorial_recursive(x):
if x<=1:
return 1
else:
return x*factorial_recursive(x-1)
print(factorial_recursive(5))
06.03
l = [1, 9, 4, 5, 16, 7]
def mean(x):
return sum(x)/len(x)
print(mean(l))
Note that in Python 3, you do not necessarily need to use the float function. See part about divisons.
07.01
# EDIT THE CODE BELOW
# Open file
f = open('../data/data.txt', 'r')
# Read and ignore header lines
header1 = f.readline()
header2 = f.readline()
header3 = f.readline()
jmag = {}
# Loop over lines and extract variables of interest
for line in f:
line = line.strip()
columns = line.split()
name = columns[2]
jmag[name] = float(columns[3])
f.close()
print(jmag['00424455+4116103'])
print('Unsorted:')
for key in jmag:
print (key, jmag[key])
print('Sorted:')
for key in sorted(jmag):
print (key, jmag[key])
07.02
# Open file
f = open('data/autofahrt.txt', 'r')
f2 = open('autofahrt_new.txt', 'w')
# read and ignore header lines
header1 = f.readline()
header2 = f.readline()
# loop over the lines in the iterable f
for line in f:
line = line.strip()
columns = line.split()
time = columns[0]
a = columns[2]
f2.write(time+' '+a+'\n') # time and a are already strings
# close the file handles
f.close()
f2.close()
08.01
import math
math.cos?
# math.cos takes radians
print('cos 60 deg = ', math.cos(math.radians(60)))
print('sin pi/6 = ', math.sin(math.pi/6))
08.02
In the first example, x is defined locally in the function by the assignment x=x*2. Any changes to x are therefore only made locally and not globally.
In the second example, x is not defined locally but x in the function points to the global x and any changes to x are therefore also visible outside the scope of the function. We could change the function to use a local copy of the global x and only change this copy in the local scope of the function:
def append_3(x):
x = x.copy()
x.append(3)
print(x)
x = [1,2]
append_3(x)
print(x)
Now we observe the same behaviour as with the function double(x).
%ls ../data/
%less ../data/munich_temperatures_average.txt
# [this works under unix only]
d = {}
max_temp = 0
with open('../data/munich_temperatures_average.txt','r') as f:
for line in f:
year, temp = line.strip().split()
s = year[0:4] # the years are the first four characters
if s not in d: # if year not found yet, add entry to dictionary
d[s] = []
d[s].append(float(temp)) # note, temp is still a string
for year in sorted(d):
temps = d[year]
print(year, min(temps), sum(temps)/float(len(temps)), max(temps))
The same for the months, assuming for simplicity that each month has 30 days:
month_names = {1: 'January',
2: 'February',
3: 'March',
4: 'April',
5: 'May',
6: 'June',
7: 'July',
8: 'August',
9: 'September',
10: 'October',
11: 'November',
12: 'December'
}
d={}
with open('../data/munich_temperatures_average.txt','r') as f:
for line in f:
year, temp = line.strip().split()
frac = float(year[4:]) # subtract number of year
month = int(12*frac) + 1 # split in 12 intervals
if month not in d: # new month in dictionary
d[month] = []
d[month].append(float(temp))
for month in sorted(d):
temps = d[month]
print(month_names[month], min(temps), sum(temps)/float(len(temps)), max(temps))