# Python: Erklärungen und Tutorials

Sequence Types — list, tuple, range

Data Structures – List – Functional Programming Tools
There are three built-in functions that are very useful when used with lists: filter(), map(), and reduce().

#### How to quit the Python prompt

To exit the prompt, press Ctrl-d if you are using IDLE or are using a Linux/BSD shell. In case of the Windows command prompt, press Ctrl-z followed by Enter.

#### shebang line

Python does not use comments except for the special case of the first line here. It is called the shebang line – whenever the first two characters of the source file are #! followed by the location of a program, this tells your Linux/Unix system that this program should be run with this interpreter when you execute the program.

#!/usr/bin/env python


#### String Note for Regular Expression Users

Always use raw strings when dealing with regular expressions. Otherwise, a lot of backwhacking may be required. For example, backreferences can be referred to as ‘\\1′ or r’\1’.

Objects

#### Indentation

Whitespace is important in Python. Actually, whitespace at the beginning of the line is important. This is called indentation. Leading whitespace (spaces and tabs) at the beginning of the logical line is used to determine the indentation level of the logical line, which in turn is used to determine the grouping of statements.
This means that statements which go together must have the same indentation. Each such set of statements is called a block. We will see examples of how blocks are important in later chapters.

### Web Application Framework

Flask is a microframework for Python based on Werkzeug, Jinja 2 and good intentions. And before you ask: It’s BSD licensed!

# Eclipse Shortcuts

CTRL + H         = C/C++ Search
CTRL + O         = Jump to Function (in the same file using a dropdown)
CTRL + SHIFT + R = Open File
CTRL + SHIFT + R = Open Resource (Files, etc.)
CTRL + SHIFT + T = Open Element (Class, Struct, etc.)


# Doppel-Bremshebel / Bremshebel für zwei Bremsen

U.S. Patent 6298744

# PHP mit FastCGI

### mod_fcgid Permission Problems

[Sun Jun 08 21:19:52 2014] [notice] Apache/2.2.27 (FreeBSD) PHP/5.5.12 mod_fcgid/2.3.9 DAV/2 configured -- resuming normal operations
[Sun Jun 08 21:19:52 2014] [info] Server built: May 31 2014 13:29:13
[Sun Jun 08 21:19:52 2014] [debug] prefork.c(1023): AcceptMutex: flock (default: flock)
[Sun Jun 08 21:19:56 2014] [info] mod_fcgid: server 10.0.0.1:/usr/local/etc/apache22/php-wrapper(60862) started
[Sun Jun 08 21:19:56 2014] [warn] [client 10.0.0.10] (53)Software caused connection abort: mod_fcgid: error reading data from FastCGI server
[Sun Jun 08 21:19:56 2014] [error] [client 10.0.0.10] Premature end of script headers: phpinfo.php
[Sun Jun 08 21:19:59 2014] [info] mod_fcgid: process /usr/local/etc/apache22/php-wrapper(60862) exit(communication error), terminated by calling exit(), return code: 255

[root@gateway /usr/local/etc/apache22]# ls -la
-rw-r--r--   1 www   www      109 Jun  8 21:12 php-wrapper

[root@gateway /usr/local/etc/apache22]# chmod 755 php-wrapper

[root@gateway /usr/local/etc/apache22]# ls -la
-rwxr-xr-x   1 www   www      109 Jun  8 21:12 php-wrapper


php5 with mod_fcgid results in 500 error – probably wrong permissions

### VirtualHost

#!/bin/sh

SUBDOMAIN=echo $USER | awk -F_ '{print$1}'

export PHPRC="$HOME/../.config/php/$SUBDOMAIN"
export PHP_FCGI_CHILDREN=4
export PHP_FCGI_MAX_REQUESTS=300:

exec /usr/local/bin/php-cgi \$@


#### Apache Module mod_fcgid

Special PHP considerations

By default, PHP FastCGI processes exit after handling 500 requests, and they may exit after this module has already connected to the application and sent the next request. When that occurs, an error will be logged and 500 Internal Server Error will be returned to the client. This PHP behavior can be disabled by setting PHP_FCGI_MAX_REQUESTS to 0, but that can be a problem if the PHP application leaks resources. Alternatively, PHP_FCGI_MAX_REQUESTS can be set to a much higher value than the default to reduce the frequency of this problem. FcgidMaxRequestsPerProcess can be set to a value less than or equal to PHP_FCGI_MAX_REQUESTS to resolve the problem.

PHP child process management (PHP_FCGI_CHILDREN) should always be disabled with mod_fcgid, which will only route one request at a time to application processes it has spawned; thus, any child processes created by PHP will not be used effectively. (Additionally, the PHP child processes may not be terminated properly.) By default, and with the environment variable setting PHP_FCGI_CHILDREN=0, PHP child process management is disabled.

The popular APC opcode cache for PHP cannot share a cache between PHP FastCGI processes unless PHP manages the child processes. Thus, the effectiveness of the cache is limited with mod_fcgid; concurrent PHP requests will use different opcode caches.

# Physik: Felder & Wellen

### Diverse

physik.hu-berlin.de: Der elektrische Strom mit Driftgeschwindigkeit, el. Leitfähigkeit (PDF)
elektronik-kompendium.de: Stromdichte
bildung-niedersachsen.de: Elektrischer Strom, Ladungsmenge und Stromdichte (gute Bilder)

### Vektoranalysis

Vektoranalysis: Teil II, mit Bild von Potential