week 10 File Reading and Plotting Flashcards
open function
sets up file as file object, retrieves input from file
how to open a file
file = open(‘data.txt’)
z = file.readlines()
helper functions
created to help set up program (ex: read file)
steps of plotting, step 1
import matlab library
import matplotlib.pyplot as plt
steps of plotting, step 2
pass value into plot function and show
plt.plot(food)
plt.show()
steps of plotting, step 3
saving plot
plt.savefig(‘plot.png’)
shorthand notation
short ways to customize plot color and marker
customizing ticks
changing the ticks on the plot
plt.xticks(ticks, regions, rotation = ‘20’)
ticks = location you want labeled
regions = new label
rotation = tilt label
plt.legend()
makes legend of lines on graph
file.close()
closes file, after called no more reads/writes allowed to file
file.read()
returns file as a string, you can specify max bytes in ()
file.readlines()
returns file lines as elements of a list
EOF
end of file
file.write()
writes string argument to file
mode
indicates how the file is opened and permissions
‘r’
open for reading
‘w’
open for writing, creates file if one doesn’t exist
‘a’
open for appending, creates file if one doesn’t exist
’ +’
can be added to letters to specify, update mode (add reading and writing)
output buffer
output is buffered by the interpreter before being written on hard drive
how to buffer output
f = open(‘myfile.txt’, ‘w’, buffering = 100)
f.flush()
clears internal buffer of a file
what type should integers be when being written to files?
integers should be converted to strings before being written or appended to files
os module
provides access to operating system
portability
ability to access an item easily, from multiple locations
how do you reduce portability?
by hardcoding file paths as string literals
path separator
’\’, ‘/’ separator between character directories
os.path.sep
stores path separator for the current operating system
os.path.join(“sub”, “output.txt”)… output?
sub\output.txt <– windows
sub/output.txt <– mac
os.walk()
walks a directory tree, iterable object in for loop
binary data
data stored as sequence of bytes
bytes object
used to represent sequence of single-byte values
bytes()
creates byte object
binary file mode ‘b’
character to open file to binary mode
header
sequence constitutes to it, describes bitmaps contents of bytes and unpacking into values
struct
module used for packing values into sequences of bytes and unpacking into values
struct.pack()
packs values (like str or int) into a sequence of bytes
byte order/endianness ‘<’
determines if the most significant or least significant value is first
strut.unpack()
unpacks sequence of bytes into new object
with statement
can be used to open file, execute statements, and close file
context manager
created by with statement, manages use of resources by setting up and tearing down operations
what is good practice to open a file?
use with so that it is closed after you’re done using it
csv file
text-based file that uses commas to separate fields
fields
data items
csv module
python library that can be used to read and write csv files
how do you read csv files?
csv.reader(csvfile, delimeter = ‘,’)
writerow()/writerows()
used to write list of strings into a csv file
numpy
python package that provides math computation tools
array
multidimensional object with ordered set of elements of the same type
shape of array
tuple of array’s dimensions
size of array
number of elements in the array
axis
direction along each array dimension
np.zeros((1, 3))
returns 1 by 3 array of zeros
np.full(shape, value)
fills shape with value
np.delete(ndarray, index, axis)
returns new array with row, col deleted
axis = 0
rows
axis = 1
columns
ndarray.sort(axis)
sorts in ascending order along specified axis
ndarray.ravel()
returns flattened version of given array
ndarray.transpose()
transposes array
np.array()
creates array
matplotlib
package to create plots
pyplot
creates figures
import structure for matplotlib
import matplotlib.pyplot as plt
plt.plot()
line plot function
plt.scatter(x,y)
scatter plot function
plt.figure(figsize = #)
creates new figure for plot to appear
plt.show()
displays figure
plt.savefig(name)
saves figure as name
plt.title()
titles plot
plt.xlabel()
labels x axis
plt.ylabel()
labels y axis
plt.text(x, y, s)
adds string ‘s’ to coordinates x,y
annotate(s, xy, xytext)
links s to coordinates xy
legend([names], loc = ‘lower right’)
adds legend with names to specified location (loc)
plt.grid(axis = ‘x’)
adds grid lines to specified axis
plt.grid(linestyle = ‘–’)
adds grid lines to both axises
plt.subplot()
multiple plots in one figure
