Merge branch 'master' of github.com:cmpitg/programming-language-notes

Author: cmpitg

Python.adoc

@@ -35,7 +35,7 @@ import hashlib
 def md5_digest(s):
     """Calculates an MD5 digest of a string."""
     m = hashlib.md5()
-    m.update("s")
+    m.update(s)
     return m.hexdigest()
 ----
 
@@ -54,7 +54,7 @@ def install(package):
 install('tornado')
 ----
 
-===  Install numpy and scipy in virtualenv
+===  Installing numpy and scipy in virtualenv
 
 For Ubuntu/Debian:
 
@@ -64,6 +64,179 @@ sudo apt-get install -y gfortran libopenblas-dev liblapack-dev
 pip install numpy scipy
 ----
 
+=== Installing PIL in virtualenv
+
+Source: http://goo.gl/NOZtUu
+
+[source,python,linenums]
+----
+sudo aptitude install libjpeg-dev
+
+sudo ln -s /usr/lib/x86_64-linux-gnu/libjpeg.so /usr/lib
+sudo ln -s /usr/lib/x86_64-linux-gnu/libfreetype.so /usr/lib
+sudo ln -s /usr/lib/x86_64-linux-gnu/libz.so /usr/lib
+
+pip install -I PIL
+----
+
+=== Using temporary file
+
+[source,python,linenums]
+----
+from tempfile import mkstemp
+from os import fdopen
+
+
+def write_temp_file(content):
+    """
+    Writes content to a temporary file and returns the file path.
+    """
+    fd, path = mkstemp()
+
+    with fdopen(fd, 'w') as out:
+        out.write(content)
+        out.write("\n")
+
+    return path
+----
+
+=== Calling method or function by name
+
+* Calling method:
++
+[source,python,linenums]
+----
+bar = getattr(foo, 'bar')
+result = method(arg_1, arg_2)
+----
+
+* Calling function:
++
+[source,python,linenums]
+----
+locals()["myfunction"]()
+# or
+globals()["myfunction"]()
+----
++
+`locals` returns a dictionary containing local symbol table. `globals`
+returns a dictionary with global symbol table.
+
+=== Trapping `Ctrl-C` but not SIGTERM
+
+By using `KeyboardInterrupt` exception:
+
+[source,python,linenums]
+----
+import time, sys
+
+
+x = 1
+while True:
+    try:
+        print(x)
+        time.sleep(.3)
+        x += 1
+    except KeyboardInterrupt:
+        print "Bye"
+        sys.exit()
+----
+
+=== Dropping into IPython PDB
+
+Install `ipdb`
+
+[source,bash,linenums]
+----
+pip install ipdb
+----
+
+
+Then in your code:
+
+[source,python,linenums]
+----
+
+import ipdb; ipdb.set_trace()
+----
+
+=== Getting site-package path
+
+[source,python,linenums]
+----
+from distutils.sysconfig import get_python_lib
+
+
+print(get_python_lib())
+----
+
+=== Generating SSH key pairs on file system
+
+Requirement: Pycrypto.
+
+[source,python,linenums]
+----
+from Crypto.PublicKey import RSA
+from tempfile import mkstemp
+from os import fdopen, chmod
+
+import stat
+
+
+def generate_RSA(bits=4096):
+    """
+    Generates an RSA keypair with an exponent of 65537.
+    """
+    new_key      = RSA.generate(bits, e=65537)
+    public_key   = new_key.publickey().exportKey("OpenSSH")
+    private_key  = new_key.exportKey("PEM")
+    return public_key, private_key
+
+
+def write_temp_file(content):
+    """
+    Writes content to a temporary file and returns the file path.
+    """
+    fd, path = mkstemp()
+
+    with fdopen(fd, 'w') as out:
+        out.write(content)
+        out.write("\n")
+
+    return path
+
+
+def gen_keys_write_files():
+    """
+    Generates an RSA key pair and writes them into 2 temporary files: one for 
+    public key and the other one for private key.
+    """
+    pub, priv = generate_RSA()
+    pub_path, priv_path = write_temp_file(pub), write_temp_file(priv)
+
+    # 644 for public key
+    chmod(pub_path, stat.S_IRUSR \
+          | stat.S_IWUSR \
+          | stat.S_IRGRP \
+          | stat.S_IROTH)
+
+    # 600 for private key
+    chmod(priv_path, stat.S_IRUSR | stat.S_IWUSR)
+
+    return pub_path, priv_path
+----
+
+=== Generating cookie secret for web framework
+
+[source,python,linenums]
+----
+import base64
+import uuid
+
+
+print(base64.b64encode(uuid.uuid4().bytes + uuid.uuid4().bytes))
+----
+
 == FAQs
 
 === Why global interpreter lock (GIL) in CPython?
@@ -113,3 +286,11 @@ the GIL. Therefore it is only in multithreaded programs that spend a lot of
 time inside the GIL, interpreting CPython bytecode, that the GIL becomes a
 bottleneck.
 ____
+
+=== IPython startup script directory
+
+Reference: http://ipython.org/ipython-doc/stable/development/config.html
+
+`$HOME/.ipython/profile_default/startup/`
+
+Just put a Python file like `00-run-something.py`.

README.adoc

@@ -20,7 +20,9 @@ List of notes:
 * link:Common-Lisp.adoc[Common Lisp] -
   http://reference-error.org/guides/Common-Lisp.html[HTML version].
 
-* link:Python.adoc[Python].
+* link:Python.adoc[Python] -
+  http://reference-error.org/guides/Python.html[HTML version].
+
 
 == License