How to Read .CSV file in Pandas

The Python Programming Language: Types and Sequences

Use type to return the object's type.

In [5]:

type('This is a string')

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Out[5]:

str

In [6]:

type(None)

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Out[6]:

NoneType

In [7]:

type(1)

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Out[7]:

int

In [8]:

type(1.0)

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Out[8]:

float

In [9]:

type(add_numbers)

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Out[9]:

function

Tuples are an immutable data structure (cannot be altered).

In [10]:

x = (1, 'a', 2, 'b')

t

tupleype(x)

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Out[10]:

tuple

Lists are a mutable data structure.

In [11]:

x = [1, 'a', 2, 'b']

type(x)

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Out[11]:

list

Use append to append an object to a list.

In [12]:

x.append(3.3)

print(x)

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[1, 'a', 2, 'b', 3.3]

This is an example of how to loop through each item in the list.

In [13]:

for item in x:

    print(item)

1
a
2
b
3.3

Or using the indexing operator:

In [14]:

i=0

while( i != len(x) ):

    print(x[i])

    i = i + 1

1
a
2
b
3.3

Use + to concatenate lists.

In [15]:

[1,2] + [3,4]

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Out[15]:

[1, 2, 3, 4]

Use * to repeat lists.

In [16]:

[1]*3

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Out[16]:

[1, 1, 1]

Use the in operator to check if something is inside a list.

In [17]:

1 in [1, 2, 3]

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Out[17]:

True

Now let's look at strings. Use bracket notation to slice a string.

In [18]:

x = 'This is a string'

print(x[0]) #first character

print(x[0:1]) #first character, but we have explicitly set the end character

print(x[0:2]) #first two characters

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T
T
Th

This will return the last element of the string.

In [19]:

x[-1]

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Out[19]:

'g'

This will return the slice starting from the 4th element from the end and stopping before the 2nd element from the end.

In [20]:

x[-4:-2]

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Out[20]:

'ri'

This is a slice from the beginning of the string and stopping before the 3rd element.

In [21]:

x[:3]

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Out[21]:

'Thi'

And this is a slice starting from the 4th element of the string and going all the way to the end.

In [22]:

x[3:]

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Out[22]:

's is a string'

In [23]:

firstname = 'Christopher'

lastname = 'Brooks'

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print(firstname + ' ' + lastname)

print(firstname*3)

print('Chris' in firstname)

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Christopher Brooks
ChristopherChristopherChristopher
True

split returns a list of all the words in a string, or a list split on a specific character.

In [24]:

firstname = 'Christopher Arthur Hansen Brooks'.split(' ')[0] # [0] selects the first element of the list

lastname = 'Christopher Arthur Hansen Brooks'.split(' ')[-1] # [-1] selects the last element of the list

print(firstname)

print(lastname)

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Christopher
Brooks

Make sure you convert objects to strings before concatenating.

In [25]:

'Chris' + 2

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---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-25-1623ac76de6e> in <module>()
----> 1 'Chris' + 2

TypeError: must be str, not int

In [26]:

'Chris' + str(2)

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Out[26]:

'Chris2'

Dictionaries associate keys with values.

In [27]:

x = {'Christopher Brooks': 'brooksch@umich.edu', 'Bill Gates': 'billg@microsoft.com'}

x['Christopher Brooks'] # Retrieve a value by using the indexing operator

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Out[27]:

'brooksch@umich.edu'

In [31]:

x['Kevyn Collins-Thompson'] = None

x['Kevyn Collins-Thompson']

x

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Out[31]:

{'Bill Gates': 'billg@microsoft.com',
 'Christopher Brooks': 'brooksch@umich.edu',
 'Kevyn Collins-Thompson': None}

Iterate over all of the keys:

In [29]:

for name in x:

    print(x[name])

brooksch@umich.edu
billg@microsoft.com
None

Iterate over all of the values:

In [32]:

for email in x.values():

    print(email)

brooksch@umich.edu
billg@microsoft.com
None

Iterate over all of the items in the list:

In [33]:

for name, email in x.items():

    print(name)

    print(email)

Christopher Brooks
brooksch@umich.edu
Bill Gates
billg@microsoft.com
Kevyn Collins-Thompson
None

You can unpack a sequence into different variables:

In [34]:

x = ('Christopher', 'Brooks', 'brooksch@umich.edu')

fname, lname, email = x

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In [35]:

fname

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Out[35]:

'Christopher'

In [36]:

lname

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Out[36]:

'Brooks'

In [37]:

email

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Out[37]:

'brooksch@umich.edu'

Make sure the number of values you are unpacking matches the number of variables being assigned.

In [38]:

x = ('Christopher', 'Brooks', 'brooksch@umich.edu', 'Ann Arbor')

fname, lname, email = x

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---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-38-9ce70064f53e> in <module>()
      1 x = ('Christopher', 'Brooks', 'brooksch@umich.edu', 'Ann Arbor')
----> 2 fname, lname, email = x

ValueError: too many values to unpack (expected 3)

In [39]:

x = ('Christopher', 'Brooks', 'brooksch@umich.edu', 'Ann Arbor')

fname, lname, email ,secondname= x

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In [40]:

secondname

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Out[40]:

'Ann Arbor'