exam 3 lec notes Flashcards
1
Q
assert statements enable you to convert _____ errors into _______ errors
A
semantic, runtime
2
Q
what is the syntax for assert ?
A
assert BOOLEAN_EXPRESSION
3
Q
what happens when assert evaluates to true? what about false?
A
true: nothing happens, moves on
false: assertion error
4
Q
what type of errors are called ‘exceptions’?
A
runtime errors
5
Q
what is ‘catching’ an expression in terms of try and except blocks?
A
where there is an exception, the try block gets terminated and the except block runs instead
6
Q
what is ‘e’ in exception?
A
the object instance, you add it after exception if you want a general overview (?) or your error
7
Q
what does str(e)?
A
gives you the reason for the exception
8
Q
whats does type(e) do?
A
gives you the type of error
9
Q
what does raising and error do in python?
A
explicitly signals something is wrong and explains the error
10
Q
what does .read() convert the contents in a file to?
A
a long str
11
Q
what needs to be explicitly written for writing in a file?
A
\n
12
Q
what does os.listdir do?
A
list all the paths and directories in a directory
13
Q
what does os.mkdir do?
A
creates a new directory
14
Q
what does os.path.isfile do?
A
returns true if a path points to a file, otherwise returns false
15
Q
what does os.path.isdir do?
A
returns true if path points to directory, otherwise it returns false
16
Q
what does os.path.join do?
A
joins one or more path components into a single path
17
Q
what is a pandas series?
A
a combination of dict and list
18
Q
what can pandas series be made from?
A
list or dict
19
Q
if the ‘exception’ is too broad in a try and except block? what could you do to try and catch a specific error?
A
you can specify the type of error you want to catch by writing the type after the exception
20
Q
what is the difference between ‘+’ and ‘append()’ method on lists?
A
+ operator creates a brand new object instance
append() modifies the existing list object instance
21
Q
what is a path on python?
A
a string that represents the location of a file or directory on a computer’s file system
22
Q
what do you pass as an argument to open(…)?
A
the relative path, you should not hardcode the ‘/’ or ‘'
23
Q
what does the read() function return?
A
the file contents as one big string
24
Q
what does calling list() on a file do?
A
converts file contents as a list
25
what needs to be explicitly written for the 'w' mode in open(...) function?
\n
26
what is os in python?
os stands for operating system, and it is a built in module that allows you to interact with the operating system and access various functions of the platform
27
what does os.path.join do?
allows you to write code in one OS platform and run it on another
28
what is pandas?
a software installed on top of python that is a package of tools for doing data science
29
what is a pandas series? what can it be created from?
a pandas series is a combination of dict and list, it can be created from either a python list or dict
30
what is an index in python series, what is an integer position in python list?
index is equivalent to a key in python dict
integer position is equivalent to index in python list
31
how would create a series using d = {'one': 7, 'two': 3}? (Syntax)
s = pd.Series(d)
or you can add the dictionary as an argument to the series
32
what is the difference between iloc and loc for Pandas series?
iloc stands for integer location, and can be used to splice the series by rows and column number
loc stands for location and is used to pick out rows and column by it's label
33
what does .quantile() do? What is its argument, and what is its defaults?
it enables to calculate percentages
it takes a argument float value between 0 and 1
it defaults to the 50th percentile
34
what does .value_counts() do?
creates a series where the key is the data, and the value is its count in the Series
default return value is descending order of counts
35
what does .sort_index() do?
sorts the series in order of values and index, returns a new series
36
what argument do you need to pass for .sorted_index() to get a series sorted in reverse order?
ascending = False
37
what are the expressions for booleans for series?
& means 'and'
I means 'or'
~ means 'not'
use () for compound boolean expressions
38
how must you format boolean expressions for a series?
specify them with a pair of []
39
what are some forms that can be created into a data frame?
- dictionary of series
- dictionary of lists
- dictionary of dictionaries
- list of dictionaries
- list of lists
40
to make a dictionary of series, what do you need to write for columns?
the names
41
what is d.loc[r] for pandas dataframe?
lookup row by row index
42
d.iloc[r] for pandas dataframe?
lookup row by row integer position
43
d[c] for pandas dataframe?
lookup column by column index
44
d.loc[r, c] for pandas dataframe?
lookup by row index and pandas column index
45
d.iloc[r c] for pandas dataframe?
lookup by row integer position and col position
46
what are two ways to set values for a specific entry in pandas dataframe (using loc and iloc)?
d.loc[r, c] = new_val
d.loc[r, c] =new_val
47
what does d[bool series] make?
a new dataframe of all rows that lined up were true
48
how do you create a dataframe from csv?
pd.read_csv("dataframe.csv")
49
what does .head(n) do for dataframe? What is the default?
it gets the first n lines, 5 is the default
50
what does .tail(n) do for dataframe? what is the default?
it gets the last n lines, 5 is default
51
what is a problem that occurs where you write a csv from pandas to file?
you may write a new index column because dataFrame already contains an index
52
how do you convert a df to a csv file?
df.to_csv('hjhsjdh.csv', index = False)
53
how do you fix double index column after converting a csv to a dataframe?
df.iloc[:, 1:]
- all rows
- columns starting from the first
54
what does HTTP status 200 mean? what about 404?
200: sucess
404: not found
55
what does .status_code() do in HTML?
it tells you whether the code was sucessful (200) or not (404)
56
what is json.load() used for?
json.load is used to read JSON data from a file object
57
what does json.loads() do?
read JSON data from a string
58
what are hyperlinks?
they are HTML Links
59
what do hyperlinks include?
an anchor (a) and hyper references (href =)
60
how do you make an unordered list and ordered list in HTML?
ul for unordered list
ol for ordered list
61
how to you add items to a HTML list?
li
62
what is table (HTML table tags)?
start and end of a table
63
what is tr (HTML table tags)?
start and end of a new row
64
how can you convert a dataframe to html using a built in function?
.to_html()
65
what does prettify() do?
it returns a formatted representation of the raw HTML
66
what does find("")?
returns the first element matching the tag string, none otherwise
67
what does find_all("") do?
returns an iterable of all matching elements (HTML 'tags'), empty iterable otherwise
68
what does get_text() do?
returns the text associated with the element if applicable, otherwise does not return
69
what does .children do? What can it be converted into?
gets children of this element, can be converted into a list
70
what is .attrs? what does it return?
is the attribute assoiciated with the tage, returns a dict of containing all attributes of the tag
71
what is the type of find's return value?
bs4.element.tag
72
what is the return type of find_all?
bs4.element.ResultSet
73
why can't you use .children on find_all but you can use it on find?
find_all returns a list where every element is given equal priority, whereas find returns a single tag object in which .children iterates to only find the specific attributes
74
What is BeautifulSoup?
a Python library used for web scraping purposes to extract the data from HTML and XML documents. It provides a simple way to navigate, search, and modify the parse tree generated from a web page
75
what does it mean to parse HTML?
to analyze it's structure and convert it into a hierarchy of nodes so the info can be easily accessed and manipulated by computer programming
76
what are the 5 steps to parsing HTML?
1. read contents from the file and make sure to close the file afterwards
2.create BeautifulSoup object instance
3.Parse the table ( if there is more than one table use find_all and extract appropriate table through indexing)
4. Parse the header
5.Parse the data rows and store data into a list of dicts
77
Are databases more structured than CSV and JSON files?
yes
78
what are the 3 requirements for databases?
1. all data contained inside one or more tables
2. all tables must be named, all columns must be named
3. all values in a column must be the same type
79
What is data transformation?
The process of changing the format, structure, or values of the data
80
What does df.set_index("column") do? What does it return?
Sets the column as the new index of reference; returns new data frame object
81
what is np.NAN?
represents 'Not a Number', basically any missing infromation
82
how do you replace Nan values in a DataFrame?
df. replace (, np.Nan)
83
what types of targets can be inputed into df.replace( target, np.Nan)?
atr, int, float, None
84
What is .isna()? what does it return?
it checks for any missing data and returns a boolean series (index on left, boolean on right)
85
what does .value_counts do?
counts the number of unique values you want, ordered in descending order
86
what does df.fillna() do? what does it return?
replaces missing values, a new dataframe
87
what does dropna() do? what does it return?
drops all the rows that contain NaN, returns new dataframe
88
What does .apply(function object reference) do? what does it return
applies an input function to every element of the Series, returns anew series objects
89
what does .groupby() do? (for pandas)
basically similar function as the SQL one, groups data by column, you will need to use aggregation methods like Sum, Avg, etc for this though
90
how do you attach the aggregation on the groupby()?
.agreggation()
91
what is the syntax for setting x-axis, y-axis, and graph titles in bar plots for matplotlib?
ax.set_xlabel()
ax.set_ylabel()
ax.set_title()
92
what is ax in matplotlib?
a general term for axis related things like x-axis, y-axis, labels, titles
93
how do you make an other column so you don't have many ticmarks on a barplot (hint: has to do with splicing the dataframe)?
1. use iloc to get the relevant rows first
2. create a new variable and set it to the sum of the other iloc rows that come after the ones in step one
3.create new column for that new variable
94
what are Axessubplots?
subplots in plots
95
if an ax = None when trying to make a Axessubplot, what is the outcome?
a new Axessubplot is created
96
what are xlim and ylim and what do you input in them?
they are limits for the x and y axis (what the smallest and largest values are for the axis)
they take either just a lower bound or (lower bound, upper bound) as a tuple
97
what is c matplotlib?
a way to color markers/lines
98
what are the x and ya xis for Series.plot.line()?
x: index
y:values
99
what is the line in Dataframe.plot.line()?
each column becomes a line
100
how do you fix a crooked line for series line plot?
sort on increasing indices,
either through sort index or sort values
101
how do you fix a crooked line for dataframe line plots?
sort on ascending order of indicies
