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NeuLab @ LTI/CMU 70

How to custom sort an alphanumeric list?

custom sort an alphanumeric list `l`

sorted(l, key=lambda x: x.replace('0', 'Z'))

Plot logarithmic axes with matplotlib in python

plot logarithmic axes with matplotlib

ax.set_yscale('log')

Access environment variables

Access environment variable "HOME"

os.environ['HOME']

Access environment variables

get value of environment variable "HOME"

os.environ['HOME']

Access environment variables

print all environment variables

print(os.environ)

Access environment variables

get all environment variables

os.environ

Access environment variables

get value of the environment variable 'KEY_THAT_MIGHT_EXIST'

print(os.environ.get('KEY_THAT_MIGHT_EXIST'))

Access environment variables

get value of the environment variable 'KEY_THAT_MIGHT_EXIST' with default value `default_value`

print(os.getenv('KEY_THAT_MIGHT_EXIST', default_value))

Access environment variables

get value of the environment variable 'HOME' with default value '/home/username/'

print(os.environ.get('HOME', '/home/username/'))

How to split a string within a list to create key-value pairs in Python

create a dictionary containing each string in list `my_list` split by '=' as a key/value pairs

print(dict([s.split('=') for s in my_list]))

finding index of an item closest to the value in a list that's not entirely sorted

find the index of element closest to number 11.5 in list `a`

min(enumerate(a), key=lambda x: abs(x[1] - 11.5))

How to use lxml to find an element by text?

find element `a` that contains string "TEXT A" in file `root`

e = root.xpath('.//a[contains(text(),"TEXT A")]')

How to use lxml to find an element by text?

Find the`a` tag in html `root` which starts with the text `TEXT A` and assign it to `e`

e = root.xpath('.//a[starts-with(text(),"TEXT A")]')

How to use lxml to find an element by text?

find the element that holds string 'TEXT A' in file `root`

e = root.xpath('.//a[text()="TEXT A"]')

Python: an efficient way to slice a list with a index list

create list `c` containing items from list `b` whose index is in list `index`

c = [b[i] for i in index]

Multiplication of 1d arrays in numpy

get the dot product of two one dimensional numpy arrays

np.dot(a[:, (None)], b[(None), :])

Multiplication of 1d arrays in numpy

multiplication of two 1-dimensional arrays in numpy

np.outer(a, b)

Execute a file with arguments in Python shell

execute a file './abc.py' with arguments `arg1` and `arg2` in python shell

subprocess.call(['./abc.py', arg1, arg2])

Pandas: Fill missing values by mean in each group faster than transfrom

Replace NaN values in column 'value' with the mean of data in column 'group' of dataframe `df`

df[['value']].fillna(df.groupby('group').transform('mean'))

Python regex alternative for join

separate each character in string `s` by '-'

re.sub('(.)(?=.)', '\\1-', s)

Python regex alternative for join

concatenate '-' in between characters of string `str`

re.sub('(?<=.)(?=.)', '-', str)

Index of element in Numpy array

get the indexes of the x and y axes in Numpy array `np` where variable `a` is equal to variable `value`

i, j = np.where(a == value)

Finding the most frequent character in a string

print letter that appears most frequently in string `s`

print(collections.Counter(s).most_common(1)[0])

How to match beginning of string or character in Python

find float number proceeding sub-string `par` in string `dir`

float(re.findall('(?:^|_)' + par + '(\\d+\\.\\d*)', dir)[0])

How to match beginning of string or character in Python

Get all the matches from a string `abcd` if it begins with a character `a`

re.findall('[^a]', 'abcd')

How to get a list of variables in specific Python module?

get a list of variables from module 'adfix.py' in current module.

print([item for item in dir(adfix) if not item.startswith('__')])

Get the first element of each tuple in a list in Python

get the first element of each tuple in a list `rows`

[x[0] for x in rows]

Get the first element of each tuple in a list in Python

get a list `res_list` of the first elements of each tuple in a list of tuples `rows`

res_list = [x[0] for x in rows]

How to repeat Pandas data frame?

duplicate data in pandas dataframe `x` for 5 times

pd.concat([x] * 5, ignore_index=True)

How to repeat Pandas data frame?

Get a repeated pandas data frame object `x` by `5` times

pd.concat([x] * 5)

Sorting JSON in python by a specific value

sort json `ips_data` by a key 'data_two'

sorted_list_of_keyvalues = sorted(list(ips_data.items()), key=item[1]['data_two'])

JSON to pandas DataFrame

read json `elevations` to pandas dataframe `df`

pd.read_json(elevations)

Generate random numbers with a given (numerical) distribution

generate a random number in 1 to 7 with a given distribution [0.1, 0.05, 0.05, 0.2, 0.4, 0.2]

numpy.random.choice(numpy.arange(1, 7), p=[0.1, 0.05, 0.05, 0.2, 0.4, 0.2])

Find maximum value of a column and return the corresponding row values using Pandas

Return rows of data associated with the maximum value of column 'Value' in dataframe `df`

df.loc[df['Value'].idxmax()]

Finding recurring patterns in a string

find recurring patterns in a string '42344343434'

re.findall('^(.+?)((.+)\\3+)$', '42344343434')[0][:-1]

convert binary string to numpy array

convert binary string '\x00\x00\x80?\x00\x00\x00@\x00\x00@@\x00\x00\x80@' to numpy array

np.fromstring('\x00\x00\x80?\x00\x00\x00@\x00\x00@@\x00\x00\x80@', dtype='<f4')

convert binary string to numpy array

convert binary string to numpy array

np.fromstring('\x00\x00\x80?\x00\x00\x00@\x00\x00@@\x00\x00\x80@', dtype='>f4')

How to use variables in SQL statement in Python?

insert variables `(var1, var2, var3)` into sql statement 'INSERT INTO table VALUES (?, ?, ?)'

cursor.execute('INSERT INTO table VALUES (?, ?, ?)', (var1, var2, var3))

How to use variables in SQL statement in Python?

Execute a sql statement using variables `var1`, `var2` and `var3`

cursor.execute('INSERT INTO table VALUES (%s, %s, %s)', (var1, var2, var3))

How to use variables in SQL statement in Python?

cursor.execute('INSERT INTO table VALUES (%s, %s, %s)', (var1, var2, var3))

pandas split string into columns

pandas split strings in column 'stats' by ',' into columns in dataframe `df`

df['stats'].str[1:-1].str.split(',', expand=True).astype(float)

pandas split string into columns

split string in column 'stats' by ',' into separate columns in dataframe `df`

df['stats'].str[1:-1].str.split(',').apply(pd.Series).astype(float)

pandas split string into columns

Unpack column 'stats' in dataframe `df` into a series of columns

df['stats'].apply(pd.Series)

wait for shell command to complete

wait for shell command `p` evoked by subprocess.Popen to complete

p.wait()

Unescaping escaped characters in a string using Python 3.2

encode string `s` to utf-8 code

s.encode('utf8')

Parse a string with a date to a datetime object

parse string '01-Jan-1995' into a datetime object using format '%d-%b-%Y'

datetime.datetime.strptime('01-Jan-1995', '%d-%b-%Y')

copy a file

copy a file from `src` to `dst`

copyfile(src, dst)

copy a file

copy file "/dir/file.ext" to "/new/dir/newname.ext"

shutil.copy2('/dir/file.ext', '/new/dir/newname.ext')

copy a file

copy file '/dir/file.ext' to '/new/dir'

shutil.copy2('/dir/file.ext', '/new/dir')

Joining a list that has Integer values with Python

print a list of integers `list_of_ints` using string formatting

print(', '.join(str(x) for x in list_of_ints))

how to multiply multiple columns by a column in Pandas

multiply column 'A' and column 'B' by column 'C' in datafram `df`

df[['A', 'B']].multiply(df['C'], axis='index')

convert string to hex in python

convert string 'a' to hex

hex(ord('a'))

How to sum the values of list to the power of their indices

Get the sum of values to the power of their indices in a list `l`

sum(j ** i for i, j in enumerate(l, 1))

Python/Django: How to remove extra white spaces & tabs from a string?

remove extra white spaces & tabs from a string `s`

""" """.join(s.split())

How to strip comma in Python string

replace comma in string `s` with empty string ''

s = s.replace(',', '')

How to resample a dataframe with different functions applied to each column?

Resample dataframe `frame` to resolution of 1 hour `1H` for timeseries index, summing values in the column `radiation` averaging those in column `tamb`

frame.resample('1H').agg({'radiation': np.sum, 'tamb': np.mean})

How do I get rid of Python Tkinter root window?

root.destroy()

Creating a Pandas dataframe from elements of a dictionary

create a pandas dataframe `df` from elements of a dictionary `nvalues`

df = pd.DataFrame.from_dict({k: v for k, v in list(nvalues.items()) if k != 'y3'})

How to obtain values of request variables using Python and Flask

Flask get value of request variable 'firstname'

first_name = request.args.get('firstname')

How to obtain values of request variables using Python and Flask

Flask get posted form data 'firstname'

first_name = request.form.get('firstname')

How to read only part of a list of strings in python

get a list of substrings consisting of the first 5 characters of every string in list `buckets`

[s[:5] for s in buckets]

how to sort by length of string followed by alphabetical order?

sort list `the_list` by the length of string followed by alphabetical order

the_list.sort(key=lambda item: (-len(item), item))

how to slice a dataframe having date field as index?

Set index equal to field 'TRX_DATE' in dataframe `df`

df = df.set_index(['TRX_DATE'])

List comprehension with an accumulator

List comprehension with an accumulator in range of 10

list(accumulate(list(range(10))))

How to convert a date string to different format

How to convert a date string '2013-1-25' in format '%Y-%m-%d' to different format '%m/%d/%y'

datetime.datetime.strptime('2013-1-25', '%Y-%m-%d').strftime('%m/%d/%y')

How to convert a date string to different format

convert a date string '2013-1-25' in format '%Y-%m-%d' to different format '%-m/%d/%y'

datetime.datetime.strptime('2013-1-25', '%Y-%m-%d').strftime('%-m/%d/%y')

How to remove multiple columns that end with same text in Pandas?

get a dataframe `df2` that contains all the columns of dataframe `df` that do not end in `prefix`

df2 = df.ix[:, (~df.columns.str.endswith('prefix'))]

Python - How to extract the last x elements from a list

create list `new_list` containing the last 10 elements of list `my_list`

new_list = my_list[-10:]

Python - How to extract the last x elements from a list

get the last 10 elements from a list `my_list`

my_list[-10:]

How to efficiently convert Matlab engine arrays to numpy ndarray?

convert matlab engine array `x` to a numpy ndarray

np.array(x._data).reshape(x.size[::-1]).T

In pandas Dataframe with multiindex how can I filter by order?

select the first row grouped per level 0 of dataframe `df`

df.groupby(level=0, as_index=False).nth(0)

How to convert list of numpy arrays into single numpy array?

concatenate sequence of numpy arrays `LIST` into a one dimensional array along the first axis

numpy.concatenate(LIST, axis=0)

How can I convert literal escape sequences in a string to the corresponding bytes?

convert and escape string "\\xc3\\x85あ" to UTF-8 code

"""\\xc3\\x85あ""".encode('utf-8').decode('unicode_escape')

How can I convert literal escape sequences in a string to the corresponding bytes?

encode string "\\xc3\\x85あ" to bytes

"""\\xc3\\x85あ""".encode('utf-8')

How do I merge two lists into a single list?

interleave the elements of two lists `a` and `b`

[j for i in zip(a, b) for j in i]

How do I merge two lists into a single list?

merge two lists `a` and `b` into a single list

[j for i in zip(a, b) for j in i]

Removing character in list of strings

delete all occureces of `8` in each string `s` in list `lst`

print([s.replace('8', '') for s in lst])

How to split a word into letters in Python

Split string `Hello` into a string of letters seperated by `,`

""",""".join('Hello')

In Django, how do I select 100 random records from the database?

in Django, select 100 random records from the database `Content.objects`

Content.objects.all().order_by('?')[:100]

Indexing one array by another in numpy

create a NumPy array containing elements of array `A` as pointed to by index in array `B`

A[np.arange(A.shape[0])[:, (None)], B]

pandas pivot table of sales

pivot dataframe `df` so that values for `upc` become column headings and values for `saleid` become the index

df.pivot_table(index='saleid', columns='upc', aggfunc='size', fill_value=0)

Confusing with the usage of regex in Python

match zero-or-more instances of lower case alphabet characters in a string `f233op `

re.findall('([a-z]*)', 'f233op')

Confusing with the usage of regex in Python

match zero-or-more instances of lower case alphabet characters in a string `f233op `

re.findall('([a-z])*', 'f233op')

Splitting a string based on a certain set of words

split string 'happy_hats_for_cats' using string '_for_'

re.split('_for_', 'happy_hats_for_cats')

Splitting a string based on a certain set of words

Split string 'sad_pandas_and_happy_cats_for_people' based on string 'and', 'or' or 'for'

re.split('_(?:for|or|and)_', 'sad_pandas_and_happy_cats_for_people')

Splitting a string based on a certain set of words

Split a string `l` by multiple words `for` or `or` or `and`

[re.split('_(?:f?or|and)_', s) for s in l]

How do I zip keys with individual values in my lists in python?

zip keys with individual values in lists `k` and `v`

[dict(zip(k, x)) for x in v]

Python how to sort this list?

Sort a list 'lst' in descending order.

sorted(lst, reverse=True)

Sorting numpy array on multiple columns in Python

sort array `order_array` based on column 'year', 'month' and 'day'

order_array.sort(order=['year', 'month', 'day'])

Sorting numpy array on multiple columns in Python

Sort a structured numpy array 'df' on multiple columns 'year', 'month' and 'day'.

df.sort(['year', 'month', 'day'])

Python: find out whether a list of integers is coherent

check if elements in list `my_list` are coherent in order

return my_list == list(range(my_list[0], my_list[-1] + 1))

Concatenate rows of pandas DataFrame with same id

group rows of pandas dataframe `df` with same 'id'

df.groupby('id').agg(lambda x: x.tolist())

Double-decoding unicode in python

encode `u'X\xc3\xbcY\xc3\x9f'` as unicode and decode with utf-8

'X\xc3\xbcY\xc3\x9f'.encode('raw_unicode_escape').decode('utf-8')

Parse String to Float or Int

parse string `a` to float

float(a)

Parse String to Float or Int

Parse String `s` to Float or Int

try: return int(s) except ValueError: return float(s)

know if an object has an attribute

check if object `a` has property 'property'

if hasattr(a, 'property'): pass

know if an object has an attribute

check if object `a` has property 'property'

if hasattr(a, 'property'): pass

know if an object has an attribute

get the value of attribute 'property' of object `a` with default value 'default value'

getattr(a, 'property', 'default value')

delete every nth row or column in a matrix using Python

delete every 8th column in a numpy array 'a'.

np.delete(a, list(range(0, a.shape[1], 8)), axis=1)

How do I create a datetime in Python from milliseconds?

convert `ms` milliseconds to a datetime object

datetime.datetime.fromtimestamp(ms / 1000.0)