Binary Numbers8 bits | 1 byte | 16 bits | word | 32 bits | double word | always at least 1 byte | add one to first number in sequence to make negative, add zeros to get full byte |
Machine Learning-program adjusts itself automatically to fit data, end result is a program trained to achieve a given task | Supervised learning-given examples of input and desired outputs, predict outputs on future unseen inputs(classification, regression, time series) | Unsupervised learning-creates a new representation of the input | Reinforcement learning-learning action to maximize payoff | Types of supervised learning tasks | 1. classification- predict which predefined set of classes and example belongs to | 2. regression - predict a real value | 2. probability estimation - estimate probability of an event | Sensitivity = fraction of positive examples predicted to be positive | TP/(TP+FN) | Specificity= proportion of negative examples predicted negative | TN/(FP+TN) | False-positive rate(FPR)= negatives predicted to be positive | FP/(FP+TN) |
SetsSet | stores an unordered set of objects, CANT BE INDEXED, no duplicates, only immutable objects contained | myset = set([]) | creates a set from a list | len(myset) | length of the set | if x in myset: | evaluates boolean condition | for element in myset: | iterate through set | for set1 = A and set2 = B, A&B = intersection | elements in common to A and B | A | B or A.union(B) | union of two sets | A-B | difference of sets, elements in A that are not in B | | | all these rules can be applied to multiple sets |
| | Integer Sequencesrange(start, end, step) | (start default is zero, step default 1) | range(5) | 0 1 2 3 4 | range(3,8) | 3 4 5 6 7 | range(len(seq)) | sequence of index of values in seq | range(2,12,3) | 2 5 8 11 |
Functionsdef functionname( arguments): | defines a function of given name with given arguments | return | only returns a certain value or string generated by the function, doesn't print, exits at this value | list = [[0 for i in range(ncols)] for j in range(nrowns)] | creates a two dimensional list of nrows and ncols filled with zeros |
Operations on Listslst = [] | creates empty list | lst.append(val) | adds item to list at end | lst.extend(seq) | add sequence of items at end | lst.insert(idx, val) | inserts item at index | lst.remove(val) | remove first item in the list with value val | lst.pop(idx) | remove and return item at index | lst.sort()/lst.reverse() | sort/reverse list in place | lst.min()/.max() | finds the min/max |
matplotlib.pyplot.plot(x,y, color) | plots the x values to x values in a certain color | .show() | shows the graph | .ylabel(name) | names y axis | .xlabel(name) | names x axis | .savefig( figname) | saves image under figname |
OOPclass | defines attributes(information we want to keep together) and methods( operations want to be able to perform on that data) | class some_class_name: | defines a class of some_class_name | def __int__(self, other attributes): | defines and initializes attributes | object.method() | calls method on an object of that class |
| | BugsSytax errors | violation of a writing rule | Exceptions(runtime) | syntax is fine, some other thing is occasionally flawed:ZeroDivisionError(can't divide by zero), NameError(can't access the variable), IndexError(When the index you are attempting to access does not exist), TypeError( operation on non-compatible type) | Logical (semantic) errors | code runs, but doesn't do what its supposed to | try: | does something that may cause an exception | except <SomeExceptionType>: | do something to handle the exception | raise[ exception object ] | raises a certain, defined type of exception | try, except, else | try something, that could cause the exception, if its fine, go to else | finally: | adds statement that happens no matter what | for a, b in zip(list 1, list 2): | iterates over elements of two lists in parallel, yields a tuple with both iterations |
File Input/Outputf = open(myfile, 'x') | opens the file, x=r for reading only, x=w for writing only, x=a for appending, x=b for file in binary format, x=wr+ reading and writing and so on | .read(size) | reads the entire file, returns a single string, size is optional number of characters | .readlines(size) | reads all lines and returns them as a list of strings | .rstrip() | returns a string with the end-of-line character(\n) removed from the end of the string | .readline() | reads single line from file, returns empty string if end of file | .close() | closes file | gzip.open() | interface to read/write compressed files, .gz extension |
Operations on Dictionariesdict = {} | sets up an empty dictionary | dict[key] = value | sets value of said at that key to value | dict[key] | calls the value at that key | del dict[key] | deletes a key from dict | dict.clear() | clears the dict of all keys | dict.update(dict2) | can update/add associations from another | dict.keys()/dict.items()/dict.values() | looks at either all keys, values, or all items in the dict | dict.pop(key) | removes element associated to that key | dict.popitem() | removes key, value pair and returns it as a tuple | dict.get(key) | returns value at that key | dict.setdefault(key) | either returns value of the key or creates the given key if not previously existent |
|
Created By
Metadata
Comments
No comments yet. Add yours below!
Add a Comment
Related Cheat Sheets