# Reference guide: Python concepts from module 1

This reference guide contains Python language introduced during module 1. The guide is organized into the following sections:

- Comments
- Functions
- Conditional statements
- Iterative statements

Within each section, items generally appear in the order they were introduced.

  
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Sections  
Comments  
Functions  
Conditional statements  
Iterative statements  
Comments  
The following syntax is used to create a comment. (A comment is a note programmers make about the intention behind their code.)  
\#  
Starts a line that contains a Python comment

\# Print approved usernames  
Contains a comment that indicates the purpose of the code that follows it is to print approved usernames  
   
Functions  
The following functions are commonly used in Python.   
print()  
Outputs a specified object to the screen

 print("login success")  
Outputs the string "login success" to the screen

print(9 < 7)  
Outputs the Boolean value of False to the screen after evaluating whether the integer 9 is less than the integer 7  
type()  
Returns the data type of its input

 print(type(51.1))  
Returns the data type of float for the input of 51.1

print(type(True))  
Returns the data type of Boolean for the input of True  
range()  
Generates a sequence of numbers

 range(0, 5, 1)  
Generates a sequence with a start point of 0, a stop point of 5, and an increment of 1; because the start point is inclusive but the stop point is exclusive, the generated sequence is 0, 1, 2, 3, and 4

range(5)  
Generates a sequence with a stop point of 5; when the start point is not specified, it is set at the default value of 0, and when the increment is not specified, it is set at the default value of 1; the generated sequence is 0, 1, 2, 3, and 4

Conditional statements  
The following keywords and operators are used in conditional statements.   
if  
Starts a conditional statement

 if device\_id != "la858zn":  
Starts a conditional statement that evaluates whether the device\_id variable contains a value that is not equal to "la858zn"

if user in approved\_list:  
Starts a conditional statement that evaluates if the user variable contains a value that is also found in the approved\_list variable  
elif  
Precedes a condition that is only evaluated when previous conditions evaluate to False; previous conditions include the condition in the if statement, and when applicable, conditions in other elif statements

 elif status == 500:  
When previous conditions evaluate to False, evaluates if the status variable contains a value that is equal to 500  
else  
Precedes a code section that only evaluates when all conditions that precede it within the conditional statement evaluate to False; this includes the condition in the if statement, and when applicable, conditions in elif statements

 else:  
When previous conditions evaluate to False, Python evaluates this else statement

   
and  
Requires both conditions on either side of the operator to evaluate to True

 if username == "bmoreno" and login\_attempts < 5:  
Evaluates to True if the value in the username variable is equal to "bmoreno" and the value in the login\_attempts variable is less than 5  
or  
Requires only one of the conditions on either side of the operator to evaluate to True

 if status == 100 or status == 102:  
Evaluates to True if the value in the status variable is equal to 100 or the value in the status variable is equal to 102  
not  
Negates a given condition so that it evaluates to False if the condition is True and to True if it is False

 if not account\_status == "removed"  
Evaluates to False if the value in the account\_status variable is equal to "removed" and evaluates to True if the value is the account\_status variable is not equal to "removed"  
Iterative statements  
The following keywords are used in iterative statements.   
for  
Signals the beginning of a for loop; used to iterate through a specified sequence

 for username in \["bmoreno", "tshah", "elarson"\]:  
Signals the beginning of a for loop that iterates through the sequence of elements in the list \["bmoreno", "tshah", "elarson"\] using the loop variable username

for i in range(10):  
Signals the beginning of a for loop that iterates through a sequence of numbers created by range(10) using the loop variable i  
while  
Signals the beginning of a while loop; used to iterate based on a condition

 while login\_attempts < 5:  
Signals the beginning of a while loop that will iterate as long as the condition that the value of login\_attempts is less than 5 evaluates to True  
break  
Used to break out of a loop  
continue  
Used to skip a loop iteration and continue with the next one