In Python, there is no need for importing external library to read and write files. Python provides an inbuilt function for creating, writing, and reading files. In this file handling in Python tutorial , we will learn:. To open a file, you need to use the built-in open function. The Python file open function returns a file object that contains methods and attributes to perform various operations for opening files in Python.
More details of these modes are explained below. With Write to file Python, you can create a. Active Oldest Votes. In python 3, import urllib. CodeGuru 3, 11 11 gold badges 50 50 silver badges 96 96 bronze badges. Ankit Jain Ankit Jain 6 6 silver badges 12 12 bronze badges. Also, check out this answer to add a progressbar to visually see your download. Add a comment.
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A classifier is trained by feeding it positive object and negative background examples. If you want to build a classifier for detecting cats, you train it with thousands of images containing cats and thousands of images that do not contain cats. This way the classifier learns to differentiate what is a cat and what is not.
You can learn more about image classification here. While building an online classifier, we do not have the luxury of having thousands of examples of the positive and negative classes. This tracker is based on an online version of AdaBoost — the algorithm that the HAAR cascade based face detector uses internally.
This classifier needs to be trained at runtime with positive and negative examples of the object. The initial bounding box supplied by the user or by another object detection algorithm is taken as a positive example for the object, and many image patches outside the bounding box are treated as the background.
Given a new frame, the classifier is run on every pixel in the neighborhood of the previous location and the score of the classifier is recorded. The new location of the object is the one where the score is maximum. So now we have one more positive example for the classifier. As more frames come in, the classifier is updated with this additional data. Pros : None. This algorithm is a decade old and works ok, but I could not find a good reason to use it especially when other advanced trackers MIL, KCF based on similar principles are available.
Cons : Tracking performance is mediocre. It does not reliably know when tracking has failed. The big difference is that instead of considering only the current location of the object as a positive example, it looks in a small neighborhood around the current location to generate several potential positive examples. The collection of images in the positive bag are not all positive examples.
Instead, only one image in the positive bag needs to be a positive example! In our example, a positive bag contains the patch centered on the current location of the object and also patches in a small neighborhood around it. Even if the current location of the tracked object is not accurate, when samples from the neighborhood of the current location are put in the positive bag, there is a good chance that this bag contains at least one image in which the object is nicely centered.
MIL project page has more information for people who like to dig deeper into the inner workings of the MIL tracker. Pros : The performance is pretty good. If you are using OpenCV 3. But if you are using a higher version, consider KCF.
Machine Learning. Data Structures. Operating System. Computer Network. Compiler Design. Computer Organization. Discrete Mathematics. Ethical Hacking. Computer Graphics.
Software Engineering. Web Technology. Cyber Security. C Programming. Control System. How can my code discover the name of an object? Is it possible to write obfuscated one-liners in Python? How do I specify hexadecimal and octal integers? How do I get int literal attribute instead of SyntaxError? How do I convert a string to a number? How do I convert a number to a string? How do I modify a string in place?
Is there a scanf or sscanf equivalent? My program is too slow. How do I speed it up? What is the most efficient way to concatenate many strings together? How do I convert between tuples and lists? How do I iterate over a sequence in reverse order? How do you remove duplicates from a list? How do you remove multiple items from a list. How do you make an array in Python? How do I create a multidimensional list? How do I apply a method to a sequence of objects? I want to do a complicated sort: can you do a Schwartzian Transform in Python?
How can I sort one list by values from another list? How do I check if an object is an instance of a given class or of a subclass of it? How do I call a method defined in a base class from a derived class that extends it? How can I organize my code to make it easier to change the base class? How do I create static class data and static class methods?
How can I overload constructors or methods in Python? How do I get a list of all instances of a given class? Why does the result of id appear to be not unique? When can I rely on identity tests with the is operator? How can a subclass control what data is stored in an immutable instance? How do I cache method calls? How do I create a. How do I find the current module name?
How can I have modules that mutually import each other? Why does this happen? Several debuggers for Python are described below, and the built-in function breakpoint allows you to drop into any of them. The pdb module is a simple but adequate console-mode debugger for Python. It is part of the standard Python library, and is documented in the Library Reference Manual.
You can also write your own debugger by using the code for pdb as an example. The PythonWin debugger colors breakpoints and has quite a few cool features such as debugging non-PythonWin programs.
PythonWin is available as part of pywin32 project and as a part of the ActivePython distribution. Komodo IDE. Pylint and Pyflakes do basic checking that will help you catch bugs sooner. Static type checkers such as Mypy , Pyre , and Pytype can check type hints in Python source code. There are a number of tools that determine the set of modules required by a program and bind these modules together with a Python binary to produce a single executable.
It converts Python byte code to C arrays; a C compiler you can embed all your modules into a new program, which is then linked with the standard Python modules.
It works by scanning your source recursively for import statements in both forms and looking for the modules in the standard Python path as well as in the source directory for built-in modules. It then turns the bytecode for modules written in Python into C code array initializers that can be turned into code objects using the marshal module and creates a custom-made config file that only contains those built-in modules which are actually used in the program.
It then compiles the generated C code and links it with the rest of the Python interpreter to form a self-contained binary which acts exactly like your script. PyInstaller Cross-platform.
PyOxidizer Cross-platform. The coding style required for standard library modules is documented as PEP 8. It can be a surprise to get the UnboundLocalError in previously working code when it is modified by adding an assignment statement somewhere in the body of a function.
This is because when you make an assignment to a variable in a scope, that variable becomes local to that scope and shadows any similarly named variable in the outer scope. Since the last statement in foo assigns a new value to x , the compiler recognizes it as a local variable.
Consequently when the earlier print x attempts to print the uninitialized local variable and an error results. This explicit declaration is required in order to remind you that unlike the superficially analogous situation with class and instance variables you are actually modifying the value of the variable in the outer scope:.
You can do a similar thing in a nested scope using the nonlocal keyword:. In Python, variables that are only referenced inside a function are implicitly global. On one hand, requiring global for assigned variables provides a bar against unintended side-effects. This clutter would defeat the usefulness of the global declaration for identifying side-effects.
You might expect that, when called, they would return, respectively, 0 , 1 , 4 , 9 , and However, when you actually try you will see that they all return 16 :.
This happens because x is not local to the lambdas, but is defined in the outer scope, and it is accessed when the lambda is called — not when it is defined. You can also verify this by changing the value of x and see how the results of the lambdas change:. This means that the value of n will be 0 in the first lambda, 1 in the second, 2 in the third, and so on. Therefore each lambda will now return the correct result:.
The canonical way to share information across modules within a single program is to create a special module often called config or cfg. Just import the config module in all modules of your application; the module then becomes available as a global name. Because there is only one instance of each module, any changes made to the module object get reflected everywhere.
For example:.
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