Course 4: Python for Data Science for AI
# Iterate through the lines of a file code
with open(example1,"r") as file1: i = 0; for line in file1: print("Iteration", str(i), ": ", line) i = i + 1;
Consider the tuple tuple1=("A","B","C" ), what is the result of the following operation tuple1[-1]?
"C" the index -1 corresponds to the last element of the tuple
What is the result of the following: Name[0] Name= "Michael Jackson"
"M" The index 0 corresponds to the first index
what is the result of the following say_what[-1] say_what=('say',' what', 'you', 'will')
"Will"
Consider the following list B=[1,2,[3,'a'],[4,'b']], what is the result of the following:B[3][1]
"b"
What is the result of the following: Name[-1] Name= "Michael Jackson"
"n" the index -1 corresponds to the last index
code to sort the tuple Ratings = (0, 9, 6, 5, 10, 8, 9, 6, 2)
# Sort the tuple Ratings = (0, 9, 6, 5, 10, 8, 9, 6, 2) RatingsSorted = sorted(Ratings) RatingsSorted
If we cast a Boolean False to an integer or float, we get
0
If we cast a Boolean False to an integer or float, we get a
0
What is the result of the following code segment:1//2
0 // corresponds to integer division
output of Dict = {"key1": 1, "key2": "2", "key3": [3, 3, 3], "key4": (4, 4, 4), ('key5'): 5, (0, 1): 6} Dict["key1"]
1
# Check the type of the values stored in numpy array code a = ["0", 1, "two", "3", 4]
a.dtype
# Get the size of numpy array a = np.array([0, 1, 2, 3, 4]) a
a.size
# Create a numpy array code
b = np.array([3.1, 11.02, 6.2, 213.2, 5.2])
type (True)
bool (short for boolean)
#code to set the fourth element and fifth element to 300 and 400 c = np.array([20, 1, 2, 3, 4])
c[3:5] = 300, 400 c
dataframce
corresponds to rows and columns of data, we can use dictionary to build it
# Slicing the numpy array code c = np.array([20, 1, 2, 3, 4])
d = c[1:4] d
the dir command
dir(RedCircle) used to get a list of the object's methods. Many of them are default Python methods.
How to get a file's name
example1 = "/resources/data/Example1.txt" file1 = open(example1, "r") file1.name
how to get the mode of the file
file1.mode
In Python 3, what is the type of the variable x after the following: x=1/1
float in Python 3, regular division always results in a float
Find the first index of "disco": genres_tuple = ("pop", "rock", "soul", "hard rock", "soft rock", \ "R&B", "progressive rock", "disco")
genres_tuple.index("disco")
Hadamard product
is a binary operation that takes two matrices of the same dimensions and produces another matrix of the same dimension as the operands where each element i, j is the product of elements i, j of the original two matrices.
A Tuple
is a sequence of immutable Python objects. Tuples are sequences, just like lists.
loc
is primarily label based; when two arguments are used, you use column headers and row indexes to select the data you want. loc can also take an integer as a row or column number.
with statement in opening files
it automatically closes the file even if the code encounters an exception. The code will run everything in the indent block then close the file object.
# Get the mean of numpy array a = np.array([1, -1, 1, -1])
mean = a.mean() mean
how would you perform the dot product between the numpy arrays u and v
np.dot(u,v)
# See the content of file code
print(FileContent)
file modes (3)
r Read mode for reading files w Write mode for writing files a for appending
We can use the double slash for integer division, where the result is
rounded
What is the result of the following: type(set([1,2,3]))
set
code to get keys inside soundtrack_dic = {"The Bodyguard":"1992", "Saturday Night Fever":"1977"}
soundtrack_dic.keys()
code to get values inside the dictionary soundtrack_dic = {"The Bodyguard":"1992", "Saturday Night Fever":"1977"}
soundtrack_dic.values()
Difference between typle and list
the tuples cannot be changed unlike lists, and tuples use parentheses, whereas lists use square brackets.
if we cast a Boolean True to an integer or float, we will get
1
what is the radius attribute after the following code block is run: RedCircle=Circle(10,'red') RedCircle.radius=1
1
# Convert list to Numpy Array a = [[11, 12, 13], [21, 22, 23], [31, 32, 33]]
A = np.array(a) A
Aliasing
A circumstance where two or more variables refer to the same object.
# Access the element on the first and second rows and third column
A[0:2, 2]
# Access the element on the first row and first and second columns (slicing) a = [[11, 12, 13], [21, 22, 23], [31, 32, 33]]
A[0][0:2]
REST API
Any API that uses Representational State Transfer (REST), which means that the two programs, on separate computers, use HTTP messages to request and transfer data.
# Write multiple lines to file code
with open('/resources/data/Example2.txt', 'w') as writefile: writefile.write("This is line A\n") writefile.write("This is line B\n")
# Makeup a numpy array within [0, 2π] and 100 elements
x = np.linspace(0, 2*np.pi, num=100)
what is the syntax to clone the list A and assign the result to list B
B=A[:]
# Get the transposed of C C = np.array([[1,1],[2,2],[3,3]])
C.T
how to read the file and assign it to a variable :
FileContent = file1.read() FileContent
Code to create the object RedCircle of type Circle
RedCircle = Circle(10, 'red')
what is the result of the following: 1=2
SyntaxError:can't assign to literal
The method append does the following:
adds one element to a list (method)
linespace function
returns evenly spaced numbers over a specified interval. We specify the starting point of the sequence and the ending point of the sequence. The parameter "num" indicates the Number of samples to generate
head()
reads first 5 rows of data
# Open file using with code
with open(example1, "r") as file1: FileContent = file1.read() print(FileContent)
# Numpy Array Multiplication by 2 y = np.array([1, 2])
z = 2 * y
# Write the strings in a list to text file code
Lines = ["This is line A\n", "This is line B\n", "This is line C\n"] Lines with open('Example2.txt', 'w') as writefile: for line in Lines: print(line) writefile.write(line)
Nest tuple example
NestedT =(1, 2, ("pop", "rock") ,(3,4),("disco",(1,2)))
# Multiply X with Y (2 dim arrays) Y = np.array([[2, 1], [1, 2]]) X = np.array([[1, 0], [0, 1]])
Z = X * Y Z
# Add X and Y 2 dimentional arrays Y = np.array([[2, 1], [1, 2]]) X = np.array([[1, 0], [0, 1]])
Z = X + Y Z
# Calculate the dot product of A and B (two dimentional arrays)
Z = np.dot(A,B) Z
Typecasting
a method of changing an entity from one data type to another. It is used in computer programming to ensure variables are correctly processed by a function.
# Acces the value of pie
np.pi
what is the type of the following array: a=np.array([0,1,7,3, 7])
numpy.ndarray
what are the keys of the following dictionary: {"a":1,"b":2}
"a","b"
iloc
is integer-based. You use column numbers and row numbers to get rows or columns at particular positions in the data frame.
# Calculate the dot product
np.dot(u, v)
# Makeup a numpy array within [-2, 2] and 5 elements
np.linspace(-2, 2, num=5)
What is the length of the list A = [1] after the following operation: A.append([2,3,4,5])
2 Append only adds one element to the list .
consider the numpy array u how would you multiply each element in the numpy array by 2
2*u
What is the result of the following: int(3.99)
3 In Python, if you cast a float to an integer, the conversion truncates towards zero, i.e.you just get rid of the numbers after the decimal place. So for 3.99 you just get rid of the ".99" leaving 3.
What is the output of the following: print("AB\nC\nDE")
AB C DE when the print function encounters a \n it displays a new line
how to close a file
file1.close()
# Create a constant to numpy array u = np.array([1, 2, 3, -1])
u + 14
Consider the following tuple A=(1,2,3,4,5), what is the result of the following:A[1:4]:
(2, 3, 4)
Consider the following Python Dictionary: Dict={"A":1,"B":"2","C":[3,3,3],"D":(4,4,4),'E':5,'F':6} What is the result of the following operation: Dict["D"]
(4, 4, 4)
# Plot numpy arrays
Plotvec1(u, z, v)
# Write line to file code
with open('/resources/data/Example2.txt', 'w') as writefile: writefile.write("This is line A")
#copy the file Example2.txt to the file Example3.txt code
with open('Example2.txt','r') as readfile: with open('Example3.txt','w') as writefile: for line in readfile: writefile.write(line)
# Read all lines and save as a list code
with open(example1, "r") as file1: FileasList = file1.readlines()
# Read one line code
with open(example1, "r") as file1: print("first line: " + file1.readline())
# Read first four characters of a file code
with open(example1, "r") as file1: print(file1.read(4))
In Python, if you executed var = '01234567', what would be the result of print(var[::2]).
0246 a stride value of 2 selects even elements
# Get the number of dimensions of numpy array a = np.array([0, 1, 2, 3, 4]) a
a.ndim
# Get the shape/size of numpy array a = np.array([0, 1, 2, 3, 4]) a
a.shape
Code to find out if album_set1 is a subset of album_set3
album_set1.issubset(album_set3)
Create a new set album_set3 that is the union of album_set1 and album_set2
album_set3 = album_set1.union(album_set2) album_set3 or album_set3 = album_set1 & (album_set2) album_set3
ndim
attribute that descrives the array dimension
code to change the first value in an array c = np.array([20, 1, 2, 3, 4]) c
c[0] = 100 c
# Verify if the file is closed code
file1.closed
What is the result of the following operation: '1,2,3,4'.split(',')
['1','2','3','4']
What is the result of the following operation: 11//2
5 the symbol // means integer value. Therefore you must round the result down.
Consider the following tuple A=(1,2,3,4,5), what is the result of the following: len(A)
5 The function len returns the number of items of a tuple.
What is the result of the following operation 3+2*2?
7 Python follows the standard mathematical conventions
In Python, if you executed name = 'Lizz', what would be the output of print(name[0:2])?
Li
sorted vs sort
The primary difference between the list sort() function and the sorted() function is that the sort() function will modify the list it is called on. The sorted() function will create a new list containing a sorted version of the list it is given. ... The sort() function modifies the list in-place and has no return value.
Consider the following set: {"A","A"}, what will the result be when the set is created
{"A"} there are no duplicate values in a set
what is the result of the following operation : {'a','b'} &{'a'}
{'a'}
read_excel
function that reads excel files
What is the result of the following: "Hello Mike".split()
["Hello","Mike"] The method split separates a string into a list based on the argument. If there is no argument as in this case the string is split using spaces.
Consider the tuple A=((11,12),[21,22]), that contains a tuple and list. What is the result of the following operation A[1]:
[21,22] the index 1 corresponds to the second element in the tuple, which contains another list.
if statement syntax
if test expression: statement(s)
# Get the biggest value in the numpy array a = np.array([1, -1, 1, -1])
max_b = b.max() max_b
code to convert the list ['rap','house','electronic music', 'rap'] to a set
set(['rap','house','electronic music','rap'])
df
short for data frames
pd
short for pandas
# Write a new line to text file with append
with open('/resources/data/Example2.txt', 'a') as testwritefile: testwritefile.write("This is line C\n")
# Read file to test if the writing worked
with open('/resources/data/Example2.txt', 'r') as testwritefile: print(testwritefile.read())
# Verify if the new line is in the text file code
with open('/resources/data/Example2.txt', 'r') as testwritefile: print(testwritefile.read())
# Calculate the production of two numpy arrays u = np.array([1, 2]) v = np.array([3, 2])
z = u * v
# Numpy Array Addition u = np.array([1, 0]) v = np.array([0, 1])
z = u + v z
