Python Training at VMWare - Day 2¶
Jan 29-31, 2018 Vikrant Patil
These notes are available online at http://notes.pipal.in/2018/vmware-pune-jan-python
© Pipal Academy LLP
In [1]:
for i in range(10):
print(i, end=",")
In [7]:
def print_primes(n):
"""
print primes less than n
"""
for i in range(2,n):
for j in range(2,i):
if i%j==0:
break
else:
print(i, end=",")
In [8]:
print_primes(20)
In [5]:
for i in range(1,20):
flag = True
for j in range(2,i):
if i%j==0:
flag = False
break
if flag:
print(i, end=",")
In [6]:
list(range(2,1))
Out[6]:
In [9]:
list(range(10)) #starts at 0 and ends at 9 at step of 1
Out[9]:
In [10]:
list(range(2,10)) #starts at 2 ends at 9 at step of 1
Out[10]:
In [11]:
list(range(1,10,2)) # starts at 1 ends at 9 at step of 2
Out[11]:
In [12]:
def print_fibonacci(n):
"""
prints fibonnaci numbers less than n
"""
prev, current = 1, 1
while current < n:
print(current, end=",")
prev, current = current, prev+current
problem
- Modify fibonacci function to print fibinacci numbers that are prime.
In [14]:
def is_prime(n):
for j in range(2,n):
if n%j==0:
return False
return True
def print_prime_fibonacci(n):
"""
prints fibonnaci numbers less than n
"""
prev, current = 1, 1
while current < n:
if is_prime(current):
print(current, end=",")
prev, current = current, prev+current
In [15]:
print_prime_fibonacci(100)
Recap lists methods¶
In [16]:
digits = list(range(10))
In [17]:
digits
Out[17]:
In [18]:
digits.append(10)
In [19]:
digits.insert(0, -1)
In [20]:
digits.pop()
Out[20]:
In [22]:
digits.pop(0)
Out[22]:
In [23]:
empty = []
In [24]:
digits[0]
Out[24]:
In [25]:
digits
Out[25]:
In [26]:
twice = []
for number in digits:
twice.append(2*number)
In [27]:
twice
Out[27]:
problems
- Write a function
squarelistwhich returns a new list which is square of every item of original list - Write a function
evenswhich returns only even numbers from given lists
In [28]:
def squarelist(items):
squares = []
for item in items:
squares.append(item**2)
return squares
def evens(items):
def even(n):
return n%2==0
e = []
for item in items:
if even(item):
e.append(item)
return e
In [29]:
squarelist(digits)
Out[29]:
In [30]:
evens(digits)
Out[30]:
lists comprehensions¶
p = []
for item in seq:
newitem = do_some_processing(item)
p.append(newitem)[do_some_processing(item) for item in seq][item for item in seq if condition(item)][do_some_processing(item) for item in seq if condition(item)]In [31]:
[x*x for x in digits]
Out[31]:
In [32]:
def cube(x):
return x*x*x
[cube(item) for item in digits]
Out[32]:
In [33]:
[cube(item) for item in digits if item%2==0]
Out[33]:
problems
- write function listpy which uses list comprehension to identify py files in given directory.
- Write a function
factorswhich finds all factors of given number (include 1 and self) - Write a function
is_primewhich checks if given number is prime based on fact that prime number has only two factors 1 and self. - Write a list comprehension to generate prime numbers.
bonus problem
- find sum of all multiples of 7 or 11 below 1000
In [34]:
def say_hello(name):
return "hello " + name
persons = ["kavya","kavita","kavi","krishna"]
[say_hello(p) for p in persons if p.endswith("i")]
[p for p in persons if p.endswith("a")]
Out[34]:
In [35]:
import os
def listpy(path):
return [file for file in os.listdir(path) if file.endswith(".py")]
In [36]:
listpy(os.getcwd())
Out[36]:
In [37]:
def factors(n):
return [i for i in range(1,n+1) if n%i==0]
In [38]:
factors(5)
Out[38]:
In [39]:
factors(25)
Out[39]:
In [40]:
def is_prime(n):
return factors(n)==[1,n]
In [41]:
is_prime(5)
Out[41]:
In [43]:
[p for p in range(50) if is_prime(p)]
Out[43]:
In [45]:
t = [[i*j for i in range(1,10)] for j in range(1,6)]
In [46]:
t
Out[46]:
In [47]:
t[0]
Out[47]:
In [48]:
t[-1]
Out[48]:
problem
- generate unit symmetric matrix of dimention 5x5 using list comprehension. unit matix is a matrix with diagonals as 1 and all other elements as zero
In [49]:
def equal(x,y):
if x==y:
return 1
else:
return 0
[[equal(i,j) for i in range(5)] for j in range(5)]
Out[49]:
In [50]:
[[int(i==j) for i in range(5)] for j in range(5)]
Out[50]:
In [52]:
[[{True:1,False:0}[i==j] for i in range(5)] for j in range(5)]
Out[52]:
In [53]:
sum([i for i in range(1000) if i%7==0 or i%11==0])
Out[53]:
In [54]:
t
Out[54]:
In [55]:
t[0] # 0th row
Out[55]:
In [56]:
t[0][0] # 0th row , 0th col
Out[56]:
In [57]:
rowcount = len(t)
In [59]:
[t[i][0] for i in range(rowcount)] # 0th column
Out[59]:
In [60]:
def column(data, n):
rowcount = len(data)
return [data[i][n] for i in range(rowcount)]
In [62]:
column(t, 0)
Out[62]:
In [63]:
column(t, 1)
Out[63]:
In [64]:
t
Out[64]:
In [65]:
def transpose(data):
columncount = len(data[0])
return [column(data, i) for i in range(columncount)]
In [66]:
transpose(t)
Out[66]:
In [67]:
t
Out[67]:
problem
- rotate 2d matrix by 90 degree clockwise.
- rotate 2d matrix by 90 degree anticlockwise
In [68]:
list(range(10))
Out[68]:
In [69]:
[i for i in range(10)]
Out[69]:
In [70]:
[10-i for i in range(10)]
Out[70]:
In [72]:
list(range(0,10,-1))
Out[72]:
In [77]:
def reverse(seq):
n = len(seq)
return [seq[n-i-1] for i in range(n)]
def rotateclockwise(data):
colcount = len(data[0])
return [reverse(column(data, i)) for i in range(colcount)]
In [78]:
list(range(10,-1,-1))
Out[78]:
In [79]:
rotateclockwise(t)
Out[79]:
In [80]:
t
Out[80]:
In [81]:
def rotateanticlockwise(data):
colcount = len(data[0])
return [column(data, i) for i in range(colcount-1, -1, -1)]
In [83]:
rotateanticlockwise(t)
Out[83]:
In [84]:
[reverse(column(t,i)) for i in range(len(t[0]))]
Out[84]:
Example¶
Quicksort
[3,6,1,2,8,9]
p = 3 less = [1,2] greater = [6,8,9]
quick(less) + [p] + quick(greater)
In [85]:
def quick(items):
if not items:
return []
pivot = items[0]
less_ = [i for i in items[1:] if i < pivot]
greater_ = [i for i in items[1:] if i >= pivot]
return quick(less_) + [pivot] + quick(greater_)
In [86]:
quick([2,3,4,1,1,2,37,1,2,1])
Out[86]:
In [89]:
import matplotlib.pyplot as plt
%matplotlib inline
def imshow(img):
plt.imshow(img, cmap=plt.cm.gray)
plt.show()
In [90]:
imshow(t)
In [91]:
imshow(rotateanticlockwise(t))
In [92]:
imshow(rotateclockwise(t))
problem
- Kaprekar iteration - you take a number find digits, reaarange them and two numbers smallest and largest. substract smallest from largest. you get new number. perform same operation on this new number.
In [95]:
def rearrangemax(n):
strn = str(n)
return int("".join(sorted(strn, reverse=True)))
def rearrangemin(n):
strn = str(n)
return int("".join(sorted(strn)))
def kaprekar(n, iters=50):
for i in range(iters):
min_ = rearrangemin(n)
max_ = rearrangemax(n)
n = max_ - min_
return n
In [96]:
kaprekar(2345)
Out[96]:
list slicing¶
slicing works on lists, string, tuples
In [97]:
digits = list(range(10))
In [98]:
digits
Out[98]:
In [99]:
digits[2:5:1] # start at 2nd index , end at 5th index(excluding) at interval of 1
Out[99]:
In [100]:
digits
Out[100]:
In [101]:
digits[:5] #first five
Out[101]:
In [102]:
digits[5:] # drop frist five
Out[102]:
In [104]:
digits[:] # copy
Out[104]:
In [107]:
digits[:-1] # all except last.. drop last one
Out[107]:
In [108]:
digits[:-3]# drop last 3
Out[108]:
In [110]:
digits[::-1] # reverse
Out[110]:
In [111]:
word = "madam"
In [112]:
f = lambda x: x*x
In [113]:
f(3)
Out[113]:
In [114]:
is_palindrom = lambda w: w==w[::-1]
In [115]:
is_palindrom(word)
Out[115]:
In [116]:
even = lambda x : x%2==0
In [117]:
even(4)
Out[117]:
In [118]:
odd = lambda x: not even(x)
In [119]:
odd(3)
Out[119]:
problem
- use slicing to write a function
split_atwhich splits given list in two lists at given index - write a function
find_extensionto find extension of given file.
In [125]:
def pair(x,y):
return 2*x, 2*y # function can return multiple values
In [121]:
pair(1,2)
Out[121]:
In [124]:
add = lambda x,y:x+y # lambda can take multiple parameters
In [126]:
add(2,3)
Out[126]:
In [129]:
f = lambda x: (x,x**2,x**3)
In [130]:
f(2)
Out[130]:
In [131]:
def split_at(seq, index):
return seq[:n],seq[n:]
In [132]:
def find_extension(filename):
return filename.split(".")[-1]
In [133]:
"hello.tar.gz".split(".")
Out[133]:
In [134]:
s = "do gees see god"
In [135]:
s[100]
In [136]:
s[:100]
Out[136]:
Iteration patterns¶
In [137]:
for n in digits:
print(n, end=",")
In [138]:
for n in reversed(digits):
print(n, end=",")
In [139]:
r = reversed(digits)
In [140]:
for i in r:
print(i, end=",")
In [141]:
for i in r:
print(i, end=",")
In [142]:
r = list(reversed(digits))
In [143]:
r
Out[143]:
In [144]:
range(10)
Out[144]:
In [147]:
for index, item in enumerate(r):
print(index, item)
In [148]:
r = range(5)
In [150]:
for i in r:
print(i)
In [151]:
for i in r:
print(i)
In [152]:
r
Out[152]:
In [153]:
digits = [1,2,3,4,5]
letter = ["A","B","C","D","E"]
In [154]:
for d,l in zip(digits, letter):
print(d, l)
In [155]:
digits = [1,2,3]
letter = ["A","B","C","D","E"]
In [157]:
list(zip([1,2],['a','b'],['x','y']))
Out[157]:
In [158]:
for d,l in zip(digits, letter):
print(d, l)
problem
- Write a function vector_add, which does vector addition of two vectors taken as list
bonus problem
- Can you write a function
zip_withwhich zips two lists with given operation?
In [159]:
def vector_add(vector1, vector2):
return [x+y for x,y in zip(vector1, vector2)]
In [160]:
def zip_with(f, v1, v2):
return [f(x,y) for x,y in zip(v1, v2)]
In [161]:
vector_add(range(5), range(5))
Out[161]:
In [162]:
zip_with(lambda x,y:x+y, range(5), range(5))
Out[162]:
In [163]:
zip_with(lambda x,y:x*y, range(5), range(5))
Out[163]:
In [168]:
%%file functions.py
def eval_poly(coeffs, x):
s = 0
n = len(coeffs)-1
for i, c in enumerate(coeffs):
s += c* x**(n-i)
return s
def eval_poly1(coeffs, x):
s = 0
for i,c in enumerate(reversed(coeffs)):
s += c*x**i
return s
def test_poly():
### [1,1,1] => x^2 + x + 1
coeffs = [1,1,1]
assert eval_poly(coeffs, 0)==1
assert eval_poly(coeffs, 1)==3
assert eval_poly([1,0,1], 2)==5
In [171]:
!py.test -v functions.py
In [166]:
0**1
Out[166]:
In [167]:
0**0
Out[167]:
String formatting¶
In [172]:
for i in range(1,11):
print(i, i**2, i**3)
In [173]:
for i in range(1,11):
print(str(i).rjust(2), str(i**2).rjust(3), str(i**3).rjust(4))
In [174]:
"wizard of {} is {}".format("oz","python")
Out[174]:
In [175]:
"wizard of {1} is {0}".format("oz","python")
Out[175]:
In [176]:
"purpose of life is {answer}, my computation in {who} says so!".format(answer=42, who="python")
Out[176]:
In [179]:
for i in range(1,11):
print("{num:2d} {sqr:3d} {cube:4d}".format(num=i, sqr=i*i, cube=i**3))
In [180]:
"{num:{digits}d}".format(num=200,digits=3)
Out[180]:
problem
- write a function to generate pascal triangle as list of lists.
```
1 1 1 1 2 1 1 3 3 1
[[1],[1,1],[1,2,1],[1,3,3,1]
```
- Write a function to prety print pascal triangle.
In [181]:
"hello".center(50)
Out[181]:
In [182]:
"hello".ljust(10)
Out[182]:
In [183]:
"23".zfill(10)
Out[183]:
In [185]:
base = [1,2,1]
[1] + [base[i]+base[i+1] for i in range(len(base)-1)] + [1]
Out[185]:
In [188]:
def pascal(n):
t = [[1]]
for i in range(1,n):
base = t[-1]
pre = [0] + base
post = base + [0]
newbase = [x+y for x,y in zip(pre,post)]
t.append(newbase)
return t
In [189]:
pascal(4)
Out[189]:
In [190]:
def pascal(n):
t = [[1]]
for i in range(1,n):
base = t[-1]
newbase = [1] + [base[i]+base[i+1] for i in range(len(base)-1)] + [1]
t.append(newbase)
return t
In [191]:
pascal(4)
Out[191]:
In [211]:
def print_pascal(t):
def format_row(row):
s = ""
for n in row:
s += "{num:{digits}d} ".format(num=n, digits=maxdigits)
return s
maxdigits = len(str(max(t[-1])))
basesize = len(t[-1])
width = maxdigits*basesize + basesize-1
for row in t:
r = format_row(row)
print(r.center(width))
In [215]:
trianlge = pascal(12)
print_pascal(trianlge)
Working with files¶
In [216]:
import this
In [217]:
%%file data.txt
The Zen of Python, by Tim Peters
Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!
In [218]:
filehandle = open("data.txt")
In [219]:
filehandle.read()
Out[219]:
In [220]:
filehandle.read()
Out[220]:
In [221]:
filehandle.close()
In [232]:
f = open("data.txt")
In [233]:
f.readline() #read only one line ...line is by default appended with \n
Out[233]:
In [234]:
f.readline()
Out[234]:
In [235]:
f.readline()
Out[235]:
In [236]:
line = f.readline()
while line:
line = f.readline()
print(line, end="")
In [241]:
f = open("data.txt")
In [242]:
f.readline()
Out[242]:
In [243]:
f.readline() ##this is empty line...
Out[243]:
In [244]:
line = f.readline()
while line:
line = f.readline()
print(line)
In [245]:
f = open("data.txt")
In [246]:
for line in f.readlines():
print(line, end="")
In [248]:
f = open("data.txt")
for index,line in enumerate(f.readlines()):
print(index+1 , line, end="")
In [249]:
for line in open("data.txt"):
print(line, end="")
problem
- write a python script cat.py which implements unix command
catapproximately. - Write a python script head.py which implements unix command
headapproximately. - Write a python script wc.py which implemtns unix command
wc
In [250]:
%%file cat.py
import sys
def cat(file):
print(open(file).read())
if __name__=="__main__":
for file in sys.argv[1:]:
cat(file)
In [251]:
!python cat.py hello.py functions.py data.txt
In [ ]:
In [256]:
%%file head.py
import sys
def head(filename, n):
f = open(filename)
for i in range(n):
print(f.readline(),end="")
if __name__ == "__main__":
head(sys.argv[2], int(sys.argv[1]))
In [257]:
!python head.py 5 data.txt
In [258]:
%%file wc.py
import sys
def count_words(file):
return len(open(file).read().split())
def count_chars(file):
return len(open(file).read())
def count_lines(file):
return len(open(file).readlines())
if __name__ == "__main__":
file = sys.argv[1]
print(count_lines(file), count_words(file), count_chars(file), file)
In [259]:
!python wc.py data.txt
problem
- find a file with max number of lines
- find a file with max number of words?
In [261]:
!python wc.py day1.html
In [262]:
!python wc.py day1.ipynb
In [263]:
!python wc.py day2.html
In [267]:
import os
[filename for filename in os.listdir(os.getcwd()) if os.path.isfile(filename)]
Out[267]:
In [268]:
files = [f for f in os.listdir(os.getcwd()) if os.path.isfile(f)]
In [269]:
import wc
In [270]:
max(files, key=wc.count_lines)
Out[270]:
In [271]:
max(files, key=wc.count_words)
Out[271]:
debuging¶
In [272]:
def add(x,y):
return x+y
In [273]:
def debug_add(x,y):
print("before add", x, y)
r = add(x,y)
print("after add", r)
return r
In [274]:
def debug(f, *args):
print("before ", f, *args)
r = f(*args)
print("after ",f, r)
return r
In [275]:
debug(add, 2,3)
Out[275]:
In [277]:
def debug(f):
def wrapper(*args):
print("before ", f, *args)
r = f(*args)
print("after ",f, r)
return r
return wrapper
In [278]:
add = debug(add)
In [279]:
add(2,3)
Out[279]:
In [ ]: