Python Fundamentals

Question 1

What are Python files called?

Answer 1

Python modules

Python files have a .py extension

Question 2

How do you write a single line comment in Python?

Answer 2

Pound sign: # comment

Correct syntax is a space between pound and text

Question 3

How do you write multiline comment in Python?

Answer 3

””” Triple Quotes “””

This is most often used in function or class documentation.

Question 4

How do you use string interpolation rather than the string format function?

Answer 4

name = “Python”

machine = “HAL”

f”Nice to meet you {name}. I am {machine}”

Note: You must put the f in front to let the interpreter know you want to use string interpolation.

Question 5

What does Python use in lieu of curly braces for code blocks?

Answer 5

Indentations to indicate blocks of code.

Question 6

What is the equality operator in Python?

Answer 6

Double equals ==

Question 7

What has a Truthy value?

Answer 7

Any number other than 0

A string as long as it is not an empty string

Question 8

What has a Falsy value?

Answer 8

The number 0

The keyword None

Question 9

What is a list like?

How do you define a list?

Answer 9

A list is very similar to an array in other languages. It is even indexed the same.

You define a list by adding empty square brackets to a variable name:

student_names = []

Question 10

What is the separator for a list?

Answer 10

The comma: student_names = [“Mark”, “Katarina”, “Jessica”]

Question 11

How do you access list elements?

Answer 11

Use bracket notation:

student_names[0] == “Mark”

list name, then index.

Question 12

How do you access the last item in a list?

Answer 12

You would use a -1 index.

student_names[-1] == “Jessica”

Second to last would be -2, and so on…

Note: Doesn’t work on a zero index going backwards. No such thing as neg. zero.

Question 13

How do you append an item to a list?

Answer 13

Use the .append() function:

student_names.append(“Homer”)

Question 14

How do you check to see if an item is in a list?

Answer 14

You just write the following:

“Mark” in student_names

This will evaluate to True

Question 15

How do you see how many items are in a list?

Answer 15

Use the len() function: len(student_names) == 4

Can use len for other items, not just exclusive to lists.

Question 16

How do you delete an element in a list?

Answer 16

use the del keyword:

del student_names[2]

Note: Elements in list will shift to the left.

Question 17

If you wanted to slice the first element out of a list, how would you do that?

Answer 17

Use the following syntax:

student_names[1:]

This skips the first element and returns everything else.

Note: This will not modify the list, just temporarily ignore elements. The list is still intact

If you want to skip the first 2, you use [2:] and so on…

Question 18

How do you ignore the first and last elements in a list?

Answer 18

Use the following syntax:

student_names[1:-1]

Remember, the last element is not zero indexed because you can’t have a negative zero number, so it’s -1

Note: This will not modify the list, just temporarily ignore elements. The list is still intact

Question 19

What are the 2 main loops in Python?

Answer 19

For Loop

While Loop

Question 20

What is the general syntax of a For loop?

Answer 20

for name in student_names:
print(“Student name is {0}”.format(name))

Note the colon at the end of the line “:” - very important

“name” can be any variable: x, name, boo, whatever…it just represents each item in the list that is being iterated over.

read as: for every “name” in the student_names list, do this…

Works like a foreach loop in other languages.

Question 21

How do you use the range function?

Answer 21

Syntax:

x = 0
for index in range(10):
x += 10
print(“The value of x is {0}”.format(x))

range(10) would mean “I want to execute this code ten times”.

The index and (10) numbers are index numbers [0, 1, 2…10]

Range supports more arguments:

range(5, 10): Start at 5 and end at 10 [5, 6, 7, 8, 9]

range(5, 10, 2): Start at 5, end at 10, but increment by 2 [5, 7, 9]

Question 22

What keyword do you use to stop the program execution at any point in your loop?

Answer 22

You use the break keyword:

ex:

for name in student_names:
if name == “Homer”:
print(“Found him! “ + name)
break
print(“Currently testing “ + name)

Break will exit the loop when the criteria tests true.

Question 23

When would you use the continue keyword?

Answer 23

When you want to skip an item in your loop.

Ex.

for name in student_names:
if name == “Bort”:
continue
print(“Found him! “ + name)
print(“Currently testing “ + name)

This will skip the name “Bort” in the list and continue through each iteration.

It says “stop executing code and continue onto the next iteration”

Question 24

How do you increment in a while loop?

Answer 24

x += 1

This will increment by 1

+= 2 will increment by two, and so on…

Question 25

What is the general syntax for a while loop?

Answer 25

x = 0 while x \< 10: print("Count is {0}".format(x)) x += 1 While checks the condition before entering the loop. You need to include a manual increment (x += 1)

Question 26

What is a Dictionary?

Answer 26

Allows you to easily store data in Key/Value pairs. Similar to JSON Syntax: student = { "name": "Mark", "student\_id": 15163 "feedback": None }

Question 27

How do you group multiple dictionaries together?

Answer 27

You would create a list of dictionaries: ex. all\_students = [ {"name": "Mark", "student\_id": 15163}, {"name": "Katarina", "student\_id": 63112}, {"name": "Jessica", "student\_id": 30021} ]

Question 28

How do you access data from a dictionary?

Answer 28

You would use bracket notation: student["name"] == "Mark" Here, "name" is the key, and "Mark" is the value of the key/value pair.

Question 29

How would you prevent a KeyError when accessing a key in a dictionary that may not exist?

Answer 29

You would provide a default value if the key was missing: student.get("last\_name", "Unknown") == "Unknown" If last\_name doesn't exist in the dictionary, then instead of throwing an error it will return "Unknown"

Question 30

How do you display all the keys in a dictionary? How about all the values?

Answer 30

student. keys() student. values() Will give you a list of all the keys or all the values in a dictionary.

Question 31

How do you change the value of a key/value pair in a dictionary?

Answer 31

student["name"] = "James" Just a simple assignment of a new value to the key.

Question 32

How do you delete a key in a dictionary?

Answer 32

del student["name"] This deletes the entire key and shifts everything to the left.

Question 33

Explain how to do error handling in Python

Answer 33

Use Try / Except code blocks: **try:** last\_name = student["last\_name"] **except KeyError:** print("Error finding last\_name") print("This code executes!") Try runs the code, and if the exception happens, it gives a graceful way of handling the error, so the code can continue running. Otherwise, the program will stop where the error happened.

Question 34

When doing exception handling, how do you chain exceptions together to check for more than one exception?

Answer 34

You just put one after another, like this: try: last\_name = student["last\_name"] numbered\_last\_name = 3 + last\_name **except KeyError:** print("Error finding last\_name") **except TypeError:** print("I can't add these two together!") print("This code executes!")

Question 35

In error handling, how do you handle errors that you don't know about?

Answer 35

You use except Exception to catch unknown errors: try: last\_name = student["last\_name"] numbered\_last\_name = 3 + last\_name except KeyError: print("Error finding last\_name") except TypeError: print("I can't add these two together!") **except Exception:** print("Unknown error")

Question 36

What if you want to know the exact error message when you are exception handling? How do you show the error?

Answer 36

Do the following: try: last\_name = student["last\_name"] numbered\_last\_name = 3 + last\_name except KeyError: print("Error finding last\_name") **except TypeError as error:** print("I can't add these two together!") **print(error)** This will print out the exact error message for you.

Question 37

When should you use exception handling?

Answer 37

Most of the time, when you are writing to a file, you should use exception handling. Also, if you feel a certain piece of code has a tendency to fail, wrap it in a try...except block. Most often failure occurs around user input.

Question 38

What is the function syntax in Python?

Answer 38

def functionname(argument): block of code **_Remember:_** * def keyword * () parenthesis * Colon: * No trailing function close characters...just indentation

Question 39

What does the return keyword do in a function?

Answer 39

It returns the result of a function run, whatever that may be. The result can be further used in other parts of the program. Contrasted with print() function, which just prints the result to the console and nothing else.

Question 40

What is a function argument? How many arguments can you have?

Answer 40

Data that you can pass to the function when it is run ``` def add\_student(name): students.append(name) ``` You can have zero, one, many, or variable number of arguments for each function.

Question 41

How do you set a default value for an argument?

Answer 41

You would add it to the argument in the function definition: ``` def add\_student(name, **student\_id=332**): students.append(name) ``` add\_student("Mark", 332) The addition of the =332 is the default value.

Question 42

What are named arguments?

Answer 42

Simply a way to make your code clearer by adding the argument name to your value when you call the function: add\_student(**name="Mark", student\_id=332**) Not necessary to do, but it makes your code more readable.

Question 43

How do you define a function with a variable number of arguments?

Answer 43

def var\_args(name, \*args) \*args allows you to put any number of arguments in the function call and Python won't complain.

Question 44

How do you use Keyword Arguments?

Answer 44

You can define arguments when you call them and it will become a key/value pair for each argument. This creates a dictionary. ``` def var\_args(name, \*\*kwargs): print(name) print(kwargs) ``` var\_args(name, a=12, b=10) print(kwargs) would return a dictionary {a:12, b:10} Note: You drop the asterisks when you use the kwargs code.

Question 45

How do you prompt for user input?

Answer 45

Use the input function: student\_name = input("Enter student name: ") This will prompt the user and assign the result to the student\_name variable.

Question 46

What is a closure?

Answer 46

A closure is when a nested function has access to the variables in the outer function.

Question 47

What happens if you use the open function in write mode to write to a file? f = open("students.txt", "w")

Answer 47

It will overwrite whatever is in the file. If you simply want to add to the file, you would use the "a" parameter instead. This will append to the file.

Question 48

Why do you need to use the .close() function after each file operation?

Answer 48

To prevent memory leaks To indicate to the OS that the file is no longer in use Some OS put a lock on a file while it is in use. Using close() will release the file.

Question 49

What is the keyword used to define a class?

Answer 49

The class keyword ## Footnote **class Student:** below, all the functions and variables associated with this class. Note: The class name is **always Capitalized.**

Question 50

What are functions in a class called?

Answer 50

Methods ## Footnote They are essentially the same thing.

Question 51

How do you create a new instance of a class?

Answer 51

Use this general syntax: ## Footnote student1 = Student()

Question 52

Explain what the self keyword is in relation to Python classes.

Answer 52

self refers to the class or variable itself. When an object is instantiated, it refers to the object itself (the current instance of the class.) When you define a class method, the first argument always has to be self: ``` class Student: def add\_student(**self,** name, student\_id=332): student = {"name": name, "student\_id": student\_id} students.append(student) ``` However, you do not have to pass the self argument when you call the method.

Question 53

What is the constructor method in Python?

Answer 53

It's a special method which gets executed every time you create a new instance of a class. by default, it's hidden, but we can create our own constructor and customize the instantiation behavior.

Question 54

How do you customize the class constructor method?

Answer 54

You define a method with the name \_\_init\_\_ ``` class Student: def \_\_init\_\_(self, name, student\_id=332): student = {"name": name, "student\_id": student\_id} students.append(student) ``` Now, when this is called, it will require the name argument and the student\_id argument. Get the idea?

Question 55

What do you need to remember when creating a class method?

Answer 55

When you define a class method, the first argument always has to be self: ``` class Student: def add\_student(self, name, student\_id=332): student = {"name": name, "student\_id": student\_id} students.append(student) ``` However, you do not have to pass the self argument when you call the method.

Question 56

Explain what a Class Attribute is

Answer 56

Simply data that can be accessed from all methods in a class. The variables are available throughout the entire instance, even when defining the methods. They are aware of any attributes in the instance. Springfield Elementary would be an example of a class attribute: class Student: school\_name = "Springfield Elementary" def \_\_init\_\_(self, name, student\_id=332): self. name = name self. student\_id = student\_id students. append(self) ``` def \_\_str\_\_(self): return "Student " + self.name ``` It is available to every method within the class to use.

Question 57

What if you want certain attributes to be the same across all instances of a class?

Answer 57

You can use a static variable. school\_name is an example of a static variable. class Student: school\_name = "Springfield Elementary" def \_\_init\_\_(self, name, student\_id=332): self. name = name self. student\_id = student\_id students. append(self) ``` def \_\_str\_\_(self): return "Student " + self.name ``` ``` def get\_name\_capitalize(self): return self.name.capitalize() ``` ``` def get\_school\_name(self): return self.school\_name ```

Question 58

If you define a method based on a class attribute, what do you need to add?

Answer 58

You need to add self when defining methods based on class attributes: ``` def get\_school\_name(self): return self.school\_name ```

Question 59

Explain class inheritance

Answer 59

Class inheritance means that you can create a second class that inherits all of the attributes and methods from the parent class. syntax: class HighSchoolStudent(Student): This will inherit everything from the Student class

Question 60

How do you override attributes or methods of a parent class in an inherited class?

Answer 60

You can just define it anew in the derived class: class HighSchoolStudent(Student): school\_name = "Springfield High School" In the Student class, school\_name was something different. You can override the behavior of the parent methods in an inherited class by simply defining the same method as in the parent class and use it in the inherited class.

Question 61

In an inherited class, can you override the derived method but still keep using the parent method as well?

Answer 61

Yes, you would use the super() keyword ``` def get\_name\_capitalize(self): original\_value = **super().get\_name\_capitalize()** return original\_value + "-HS" ``` in this code, we pull the original .get\_name\_capitalize() method and add something to it without having to rewrite the entire method.

Question 62

When you break your program up into different modules or if you are using a third party library, how do you import it into your main python program?

Answer 62

You can use the import keyword: from module\_name import \* The asterisk means "import everything" (Sometimes this isn't the best strategy...it can result in namespace issues) You can import individual classes or functions or methods as well instead of everything by listing them explicitly.

Question 63

What is the most popular Python framework?

Answer 63

django It powers sites like Instagram, Pinterest, the Onion, NASA, and others.

Question 64

What is a GET request?

Answer 64

When you fetch a web page or web element

Question 65

What is a POST request?

Answer 65

When you send data to a web server ex. Submitting a form

Question 66

What are Python virtual environments?

Answer 66

Virtual environments allow you to set up independent Python environments. For ex: You cannot have two Django environments installed on same machine...you'll get a version conflict. With virtual environments, however, you can have both versions of Django on your machine and they don't care about each other. They are completely isolated from one another.

Question 67

How do you install the virtual environments module? How do you create a new virtual environment?

Answer 67

From command line: You install virtual environments using pip command: **pip install virtualenv** Create a virtual environment: **virtualenv **

Question 68

How do you specify the Python version you want your virtual environment to use?

Answer 68

Command: virtualenv --python=python2.7 --python is a flag

Question 69

How do you activate your virtual environment?

Answer 69

command: $source /bin/activate If successful, prompt will be prefixed with the virtual env name: (env\_name) $

Question 70

If you install packages using pip in a certain virtual environment, are they active anywhere else?

Answer 70

No. They are only installed to the single virtual environment. They will not be active anywhere else, not even the global Python environment.

Question 71

How do you exit a virtual environment?

Answer 71

Simply type this command: deactivate

Question 72

How do you use PyCharm to set up virtual environments?

Answer 72

In PyCharm settings, search for "interpreter options"

Question 73

What is a breakpoint? How do you set a breakpoint in PyCharm?

Answer 73

Line in our code that when reached will pause execution of the program and allow you to inspect the programming environment. In PyCharm, you just click to the right of the line number and a breakpoint will be set.

Question 74

What program can you use to create executable files for your Python program?

Answer 74

Software is called pyinstaller. How to use it: pip install pyinstaller navigate to path where Python code lives type pyinstaller main.pi (whatever your main file is) and hit Enter Pyinstaller takes care of associated modules and packages them. You can use the --onefile flag if you want to package just one file