COSC code

print(x)

Prints the value of x.

return x

Sends x back as the function result.

def f(x):

Defines a function with parameter x.

x = 5

Assigns the value 5 to x.

x == 5

Checks whether x is equal to 5.

x != 5

Checks whether x is not equal to 5.

x < 5

Checks whether x is less than 5.

x <= 5

Checks whether x is less than or equal to 5.

if condition:

Runs the indented code only if condition is True.

elif condition:

Checks another condition if previous if/elif was False.

else:

Runs if all previous conditions were False.

while condition:

Repeats while condition is True.

count += 1

Increases count by 1.

total += value

Adds value to total.

for item in items:

Loops through each item in items.

for i in range(len(items)):

Loops through every index of items.

range(n)

Produces 0 up to n - 1.

range(a, b)

Produces a up to b - 1.

items[i]

Gets item at index i.

items[-1]

Gets the last item.

items[a:b]

Gets items from index a up to b - 1.

items[::-1]

Returns a reversed copy of the list.

items.append(x)

Adds x to the end of the list.

items.sort()

Sorts the list in place.

items.reverse()

Reverses the list in place and returns None.

items.pop()

Removes and returns the last item.

len(items)

Returns the number of items.

x in items

Checks whether x is in items.

result = []

Creates an empty list.

result = ""

Creates an empty string.

result += text

Adds text onto the end of result.

tuple_value = (x, y)

Creates a tuple containing x and y.

x, y = point

Unpacks a 2-item tuple into x and y.

open(filename)

Opens a file and returns a file object.

infile.read()

Reads the entire file as one string.

infile.close()

Closes the file.

text.splitlines()

Splits text into a list of lines.

line.split(",")

Splits a CSV line into a list of strings.

s.strip()

Removes whitespace from both ends.

s.upper()

Returns uppercase version of s.

s.lower()

Returns lowercase version of s.

s.title()

Returns title-case version of s.

s.startswith(prefix)

Checks whether s starts with prefix.

int(text)

Converts text to an integer.

float(text)

Converts text to a float.

try:

Starts a block where an error might happen.

except ValueError:

Runs if a ValueError occurs in the try block.

pass

Does nothing.

raise RuntimeError("message")

Creates and raises a RuntimeError.

d = {}

Creates an empty dictionary.

d[key]

Gets the value stored under key.

d[key] = value

Adds or updates a key-value pair.

key in d

Checks whether key exists in the dictionary.

d.get(key, default)

Gets d[key], or default if key is missing.

d.items()

Gives key-value pairs from the dictionary.

d.keys()

Gives the dictionary keys.

d.values()

Gives the dictionary values.

counts[item] = counts.get(item, 0) + 1

Counts how many times item appears.

if key not in d: d[key] = []

Creates an empty list for a new dictionary key.

d[key].append(value)

Adds value to the list stored at d[key].

s = set()

Creates an empty set.

set(items)

Creates a set of unique items from items.

s.add(item)

Adds item to the set.

item in s

Checks whether item is in the set.

sorted(items)

Returns a sorted list.

class Person:

Defines a new class/type called Person.

def __init__(self, ...):

Initialises a new object.

self.x = x

Stores x as an attribute of the object.

obj.x

Accesses the x attribute of obj.

obj.method()

Calls a method on obj.

def __str__(self):

Defines what print(object) shows.

def __repr__(self):

Defines the programmer-style representation.

items.sort(key=lambda x: x.name)

Sorts objects by their name attribute.

import numpy as np

Imports NumPy as np.

np.array([1, 2, 3])

Creates a NumPy array.

np.zeros(n)

Creates an array of n zeros.

np.ones(n)

Creates an array of n ones.

np.full(n, x)

Creates an array of n copies of x.

np.arange(start, stop, step)

Creates values from start up to but not including stop.

np.linspace(start, stop, n)

Creates n evenly spaced values including start and stop.

xs ** 2

Squares every value in a NumPy array.

np.exp(xs)

Applies exponential to every value in xs.

data[:, 0]

Gets column 0 from a 2D NumPy array.

data[0, :]

Gets row 0 from a 2D NumPy array.

data[:, 1:]

Gets all rows and columns from column 1 onwards.

data[data > 0]

Filters data to values greater than 0.

np.logical_and(a, b)

Combines two boolean arrays with AND.

np.loadtxt(filename, delimiter=",", skiprows=1)

Loads numeric CSV data into a NumPy array.

np.loadtxt(filename, usecols=2)

Loads only column 2.

np.sum(data)

Returns the sum of data.

np.mean(data)

Returns the average of data.

np.min(data)

Returns the minimum value.

np.max(data)

Returns the maximum value.

np.std(data)

Returns the standard deviation.

from matplotlib import pyplot as plt

Imports plotting tools.

axes = plt.axes()

Creates graph axes.

axes.plot(xs, ys)

Plots y-values against x-values.

axes.bar(xs, ys)

Draws a bar chart.

axes.hist(data, bins=bins)

Draws a histogram.

axes.set_title(title)

Sets the graph title.