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  • Problem making local copy of a webpage

    - by Claudiu
    I want to run this chrome experiment locally. I copied the .html and .js files, along with the two .jpgs that the demo uses. However, when I run it off my local drive, Chrome gives this error: light.js:89 - Uncaught Error: SECURITY_ERR: DOM Exception 18 Line 89 returns the image data from the canvas after drawing the image to it. What's causing this security exception? It seems to not be Chrome-specific, as Firefox gives the same error.

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  • Derivative of a Higher-Order Function

    - by Claudiu
    This is in the context of Automatic Differentiation - what would such a system do with a function like map, or filter - or even one of the SKI Combinators? Example: I have the following function: def func(x): return sum(map(lambda a: a**x, range(20))) What would its derivative be? What will an AD system yield as a result? (This function is well-defined on real-number inputs).

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  • In C, do braces act as a stack frame?

    - by Claudiu
    If I create a variable within a new set of curly braces, is that variable popped off the stack on the closing brace, or does it hang out until the end of the function? For example: void foo() { int c[100]; { int d[200]; } //code that takes a while return; } Will d be taking up memory during the code that takes a while section?

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  • in-memory database in Python

    - by Claudiu
    I'm doing some queries in Python on a large database to get some stats out of the database. I want these stats to be in-memory so other programs can use them without going to a database. I was thinking of how to structure them, and after trying to set up some complicated nested dictionaries, I realized that a good representation would be an SQL table. I don't want to store the data back into the persistent database, though. Are there any in-memory implementations of an SQL database that supports querying the data with SQL syntax?

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  • Python + PostgreSQL + strange ascii = UTF8 encoding error

    - by Claudiu
    I have ascii strings which contain the character "\x80" to represent the euro symbol: >>> print "\x80" € When inserting string data containing this character into my database, I get: psycopg2.DataError: invalid byte sequence for encoding "UTF8": 0x80 HINT: This error can also happen if the byte sequence does not match the encodi ng expected by the server, which is controlled by "client_encoding". I'm a unicode newbie. How can I convert my strings containing "\x80" to valid UTF-8 containing that same euro symbol? I've tried calling .encode and .decode on various strings, but run into errors: >>> "\x80".encode("utf-8") Traceback (most recent call last): File "<pyshell#14>", line 1, in <module> "\x80".encode("utf-8") UnicodeDecodeError: 'ascii' codec can't decode byte 0x80 in position 0: ordinal not in range(128)

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  • pyparsing ambiguity

    - by Claudiu
    I'm trying to parse some text using PyParser. The problem is that I have names that can contain white spaces. So my input might look like this: Joe Bob Jimmy Foo Joe decides to eat. Bob decides to not eat. Jimmy Foo decides to eat. How can I create a parser for the decides to eat line? If I create my name parser naively, meaning with alphabetic characters plus space characters, then it will match the entire line.

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  • Fibonacci Code Golf

    - by Claudiu
    Generate the Fibonacci sequence in the fewest amount of characters possible. Any language is OK, except for one that you define with one operator, f, which prints the Fibonacci numbers. Starting point: 25 characters in Haskell: f=0:1:zipWith(+)f(tail f)

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  • SQL get data out of BEGIN; ...; END; block in python

    - by Claudiu
    I want to run many select queries at once by putting them between BEGIN; END;. I tried the following: cur = connection.cursor() cur.execute(""" BEGIN; SELECT ...; END;""") res = cur.fetchall() However, I get the error: psycopg2.ProgrammingError: no results to fetch How can I actually get data this way? Likewise, if I just have many selects in a row, I only get data back from the latest one. Is there a way to get data out of all of them?

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  • shared global variables in C

    - by Claudiu
    How can I create global variables that are shared in C? If I put it in a header file, then the linker complains that the variables are already defined. Is the only way to declare the variable in one of my C files and to manually put in externs at the top of all the other C files that want to use it? That sounds not ideal.

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  • gcc run "light" preprocessor

    - by Claudiu
    Is there any way to run the gcc preprocessor, but only for user-defined macros? I have a few one-liners and some #ifdef etc... conditionals, and I want to see what my code looks like when just those are expanded. As it is, the includes get expanded, my fprintf(stderr)s turn into fprintf(((__getreeent())-_stderr), etc...

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  • What percent of web sites use JavaScript?

    - by Claudiu
    I'm wondering just how pervasive JavaScript is. This article states that 73% of websites they tested rely on JavaScript for important functionality, but it seems to me that the number must be larger. Have any surveys been done on this topic? Maybe a better way to phrase this question is - are there any sites that don't use JavaScript? EDIT: By 'use', I don't necessarily mean "rely on for important functionality" - that was just the statistic that one article gave.

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  • sql combine two subqueries

    - by Claudiu
    I have two tables. Table A has an id column. Table B has an Aid column and a type column. Example data: A: id -- 1 2 B: Aid | type ----+----- 1 | 1 1 | 1 1 | 3 1 | 1 1 | 4 1 | 5 1 | 4 2 | 2 2 | 4 2 | 3 I want to get all the IDs from table A where there is a certain amount of type 1 and type 3 actions. My query looks like this: SELECT id FROM A WHERE (SELECT COUNT(type) FROM B WHERE B.Aid = A.id AND B.type = 1) = 3 AND (SELECT COUNT(type) FROM B WHERE B.Aid = A.id AND B.type = 3) = 1 so on the data above, just the id 1 should be returned. Can I combine the 2 subqueries somehow?

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  • Why is Postgres doing a Hash in this query?

    - by Claudiu
    I have two tables: A and P. I want to get information out of all rows in A whose id is in a temporary table I created, tmp_ids. However, there is additional information about A in the P table, foo, and I want to get this info as well. I have the following query: SELECT A.H_id AS hid, A.id AS aid, P.foo, A.pos, A.size FROM tmp_ids, P, A WHERE tmp_ids.id = A.H_id AND P.id = A.P_id I noticed it going slowly, and when I asked Postgres to explain, I noticed that it combines tmp_ids with an index on A I created for H_id with a nested loop. However, it hashes all of P before doing a Hash join with the result of the first merge. P is quite large and I think this is what's taking all the time. Why would it create a hash there? P.id is P's primary key, and A.P_id has an index of its own.

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  • Find most significant bit (left-most) that is set in a bit array

    - by Claudiu
    I have a bit array implementation where the 0th index is the MSB of the first byte in an array, the 8th index is the MSB of the second byte, etc... What's a fast way to find the first bit that is set in this bit array? All the related solutions I have looked up find the first least significant bit, but I need the first most significant one. So, given 0x00A1, I want 9.

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  • sql generate unique table/view name

    - by Claudiu
    I want to create some mad robust code. I want to take a query as a string, create a temporary view / table to store the results, use it, then drop the table. I want to use a name that is guaranteed to not already exist in the database. Is there an SQL command to generate a unique table name? I'm using postgresql if this is implementation-specific.

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  • PostgreSQL function to iterate through/act on many rows with state

    - by Claudiu
    I have a database with columns looking like: session | order | atype | amt --------+-------+-------+----- 1 | 0 | ADD | 10 1 | 1 | ADD | 20 1 | 2 | SET | 35 1 | 3 | ADD | 10 2 | 0 | SET | 30 2 | 1 | ADD | 20 2 | 2 | SET | 55 It represents actions happening. Each session starts at 0. ADD adds an amount, while SET sets it. I want a function to return the end value of a session, e.g. SELECT session_val(1); --returns 45 SELECT session_val(2); --returns 55 Is it possible to write such a function/query? I don't know how to do any iteration-like things with SQL, or if it's possible at all.

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  • bash "map" equivalent: run command on each file

    - by Claudiu
    I often have a command that processes one file, and I want to run it on every file in a directory. Is there any built-in way to do this? For example, say I have a program data which outputs an important number about a file: ./data foo 137 ./data bar 42 I want to run it on every file in the directory in some manner like this: map data `ls *` ls * | map data to yield output like this: foo: 137 bar: 42

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  • get n records at a time from a temporary table

    - by Claudiu
    I have a temporary table with about 1 million entries. The temporary table stores the result of a larger query. I want to process these records 1000 at a time, for example. What's the best way to set up queries such that I get the first 1000 rows, then the next 1000, etc.? They are not inherently ordered, but the temporary table just has one column with an ID, so I can order it if necessary. I was thinking of creating an extra column with the temporary table to number all the rows, something like: CREATE TEMP TABLE tmptmp AS SELECT ##autonumber somehow##, id FROM .... --complicated query then I can do: SELECT * FROM tmptmp WHERE autonumber>=0 AND autonumber < 1000 etc... how would I actually accomplish this? Or is there a better way? I'm using Python and PostgreSQL.

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  • create temporary table from cursor

    - by Claudiu
    Is there any way, in PostgreSQL accessed from Python using SQLObject, to create a temporary table from the results of a cursor? Previously, I had a query, and I created the temporary table directly from the query. I then had many other queries interacting w/ that temporary table. Now I have much more data, so I want to only process 1000 rows at a time or so. However, I can't do CREATE TEMP TABLE ... AS ... from a cursor, not as far as I can see. Is the only thing to do something like: rows = cur.fetchmany(1000); cur2 = conn.cursor() cur2.execute("""CREATE TEMP TABLE foobar (id INTEGER)""") for row in rows: cur2.execute("""INSERT INTO foobar (%d)""" % row) or is there a better way? This seems awfully inefficient.

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