Write a program in python asking the user to input a list and if it contains integers, show the square of it in the output and if there are strings do swap case.
[ the entering list should contain both int and string]
Answers
Explanation:
Values and data types
A value is one of the fundamental things — like a letter or a number — that a program manipulates. The values we have seen so far are 2 (the result when we added 1 + 1), and "Hello, World!".
These values belong to different data types: 2 is an integer, and "Hello, World!" is a string, so-called because it contains a string of letters. You (and the interpreter) can identify strings because they are enclosed in quotation marks.
The print statement also works for integers.
>>> print 4
4
If you are not sure what type a value has, the interpreter can tell you.
>>> type("Hello, World!")
<type 'str'>
>>> type(17)
<type 'int'>
Not surprisingly, strings belong to the type str and integers belong to the type int. Less obviously, numbers with a decimal point belong to a type called float, because these numbers are represented in a format called floating-point.
>>> type(3.2)
<type 'float'>
What about values like "17" and "3.2"? They look like numbers, but they are in quotation marks like strings.
>>> type("17")
<type 'str'>
>>> type("3.2")
<type 'str'>
They’re strings.
Strings in Python can be enclosed in either single quotes (‘) or double quotes (”):
>>> type('This is a string.')
<type 'str'>
>>> type("And so is this.")
<type 'str'>
Double quoted strings can contain single quotes inside them, as in "Bruce's beard", and single quoted strings can have double quotes inside them, as in 'The knights who say "Ni!"'.
When you type a large integer, you might be tempted to use commas between groups of three digits, as in 1,000,000. This is not a legal integer in Python, but it is legal:
>>> print 1,000,000
1 0 0
Well, that’s not what we expected at all! Python interprets 1,000,000 as a list of three items to be printed. So remember not to put commas in your integers.
2.2. Variables
One of the most powerful features of a programming language is the ability to manipulate variables. A variable is a name that refers to a value.
The assignment statement creates new variables and gives them values:
>>> message = "What's up, Doc?"
>>> n = 17
>>> pi = 3.14159
This example makes three assignments. The first assigns the string "What's up, Doc?" to a new variable named message. The second gives the integer 17 to n, and the third gives the floating-point number 3.14159 to pi.
The assignment operator, =, should not be confused with an equals sign (even though it uses the same character). Assignment operators link a name, on the left hand side of the operator, with a value, on the right hand side. This is why you will get an error if you enter:
>>> 17 = n
A common way to represent variables on paper is to write the name with an arrow pointing to the variable’s value. This kind of figure is called a state diagram because it shows what state each of the variables is in (think of it as the variable’s state of mind). This diagram shows the result of the assignment statements:
State diagram
The print statement also works with variables.
>>> print message
What's up, Doc?
>>> print n
17
>>> print pi
3.14159
In each case the result is the value of the variable. Variables also have types; again, we can ask the interpreter what they are.
>>> type(message)
<type 'str'>
>>> type(n)
<type 'int'>
>>> type(pi)
<type 'float'>
The type of a variable is the type of the value it refers to.
2.3. Variable names and keywords
Programmers generally choose names for their variables that are meaningful — they document what the variable is used for.
Variable names can be arbitrarily long. They can contain both letters and numbers, but they have to begin with a letter. Although it is legal to use uppercase letters, by convention we don’t. If you do, remember that case matters. Bruce and bruce are different variables.
The underscore character ( _) can appear in a name. It is often used in names with multiple words, such as my_name or price_of_tea_in_china.
If you give a variable an illegal name, you get a syntax error:
>>> 76trombones = "big parade"
SyntaxError: invalid syntax
>>> more$ = 1000000
SyntaxError: invalid syntax
>>> class = "Computer Science 101"
SyntaxError: invalid syntax
76trombones is illegal because it does not begin with a letter. more$ is illegal because it contains an illegal character, the dollar sign. But what’s wrong with class?
It turns out that class is one of the Python keywords. Keywords define the language’s rules and structure, and they cannot be used as variable names.
Python has thirty-one keywords:
and as assert break class continue
def del elif else except exec
finally for from global if import
in is lambda not or pass
print raise return try while with
yield
You might want to keep this list handy. If the interpreter complains about one of your variable names and you don’t know why, see if it is on this list