# Expressions

Definition: An expression is an construct of symbols that the python interpreter can evaluate. The expression we can type in the inpreter, and that the interpreter can evaluate meaningfully are

• numerical expressions
• textual expressions
• logical expressions

## Numerical Expression

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In [1]:

x = 5; y = 700; z = 821

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In [2]:

x + y
x * y
x ** y

# etc.

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Out[2]:

1901091566295159823515072405835103109264871206373519032441746057565854249277472203557201497052621863202610629503298188674778262443788623503544624583852527978187847081031734592912357695384795280342176118255040207774382160198963856151525515423826657984269000422536358621400702420807052018353350982292716419484982535110142249297056924906488555403892140062791926661918530613262656492971667990518503399759909868494802563030058676203176091173708076110583121975938780678916373290121555328369140625L

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## Textual Expression

The simplest "textual expression" is a string, i.e., a sequence of characters (i.e., alphanumeric symbols, plus puntuation marks, plus special escape sequences).

To let python Know that your text is a string, and not the name of a variable, you need to use quotes:

• single quotes: '
• double quotes: "
• triple quotes: """
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In [3]:

"Once upon a time\nthere was a little rabbit\nwho liked carrots two much."

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Out[3]:

'Once upon a time\nthere was a little rabbit\nwho liked carrots two much.'

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In [4]:

"""Once upon a time
there was a little rabbit
who liked carrots two much
He said
I'd live another carrot"""

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Out[4]:

"Once upon a time\nthere was a little rabbit\nwho liked carrots two much\nHe said\nI'd live another carrot"

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### Operations on strings

``````

In [8]:

x = "Benoit"
y = "Dherin"

z = x + ' ' + y
print z

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Benoit Dherin

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In [12]:

x = "Hello "
8*x

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Out[12]:

'Hello Hello Hello Hello Hello Hello Hello Hello '

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### String formatting

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In [25]:

name = 'Bob'; age = 32; job ='Teacher'; teeth = 12.5
name2 = 'Marcelluscatapultus'; age2 = 3320; job2 ='Yogi'; teeth2 = 122.82

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In [26]:

print name + job + str(age) + str(teeth)

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BobTeacher3212.5

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In [41]:

formatted_string  = "| %-20s | %-20s | %-4d | %-8.2f |" % (name, job, age, teeth)
formatted_string2 = "| %-20s | %-20s | %-4d | %-8.2f |" % (name2, job2, age2, teeth2)

print '_'* 65
print formatted_string
print formatted_string2
print '_'* 65

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_________________________________________________________________
| Bob                  | Teacher              | 32   | 12.50    |
| Marcelluscatapultus  | Yogi                 | 3320 | 122.82   |
_________________________________________________________________

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## Logical Expression

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In [ ]:

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In [6]:

True

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Out[6]:

True

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In [7]:

False

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Out[7]:

False

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In [20]:

x = True; y = False

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In [23]:

x and y

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Out[23]:

False

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In [24]:

x or y

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Out[24]:

True

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In [25]:

not x

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Out[25]:

False

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In [26]:

(x or y) and not x

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Out[26]:

False

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In [ ]:

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