Difference between revisions of "Python quick reference"
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'''assigenment examples''' | '''assigenment examples''' | ||
| + | ====simple string assignment==== | ||
<source lang="python"> | <source lang="python"> | ||
>>> var1 = 'foo' | >>> var1 = 'foo' | ||
| + | </source> | ||
| + | |||
| + | this automatically creates a variable of type string | ||
| + | |||
>>> type(var1) | >>> type(var1) | ||
<type 'str'> | <type 'str'> | ||
| + | |||
| + | printing your variable... | ||
| + | |||
| + | <source lang="python"> | ||
>>> print var1 | >>> print var1 | ||
foo | foo | ||
| Line 19: | Line 28: | ||
example: | example: | ||
| + | |||
| + | >>> var1 = foo | ||
| + | Traceback (most recent call last): | ||
| + | File "<stdin>", line 1, in ? | ||
| + | NameError: name 'foo' is not defined | ||
| + | |||
| + | ====integer variable==== | ||
<source lang="python"> | <source lang="python"> | ||
| − | >>> var1 = foo | + | >>> my_int_var1 = 1 |
| + | >>> print my_int_var1 | ||
| + | 1 | ||
| + | </source> | ||
| + | |||
| + | ====assigning a variable to another variable==== | ||
| + | |||
| + | <source lang="python"> | ||
| + | >>> var2 = 'bar' | ||
| + | >>> var1 = var2 | ||
| + | >>> print var1 | ||
| + | bar | ||
| + | </source> | ||
| + | |||
| + | muli-variable example: | ||
| + | |||
| + | <source lang="python"> | ||
| + | >>> var1 = 'foo' | ||
| + | >>> var2 = 'bar' | ||
| + | >>> new_var = "%s %s" % (var1,var2) | ||
| + | >>> print new_var | ||
| + | foo bar | ||
</source> | </source> | ||
| − | |||
| − | |||
| − | |||
===print=== | ===print=== | ||
print sing variable named foo | print sing variable named foo | ||
| − | + | <source lang="python"> | |
| + | >>> print foo | ||
| + | </source> | ||
| − | print | + | print variables with text |
| − | + | <source lang="python"> | |
| + | print 'my variable is %s' % FOO | ||
| + | </source> | ||
| + | or | ||
| + | <source lang="python"> | ||
| + | print 'my variable are %s %s' % (FOO, BAR) | ||
| + | </source> | ||
| + | |||
| + | print without a newline, use comma at the end of the print statement | ||
| + | <source lang="python"> | ||
| + | for i in range(10): | ||
| + | ... print i, | ||
| + | ... else: | ||
| + | ... print | ||
| + | ... | ||
| + | 0 1 2 3 4 5 6 7 8 9 | ||
| + | </source> | ||
==Common string operations== | ==Common string operations== | ||
print nth word of string | print nth word of string | ||
| + | <source lang="python"> | ||
print s.split()[n] | print s.split()[n] | ||
| + | </source> | ||
| + | |||
| + | <source lang="python"> | ||
| + | str = "this is string example....wow!!!" | ||
| + | print (str.split( )) | ||
| + | print (str.split('i',1)) | ||
| + | print (str.split('w')) | ||
| + | </source> | ||
| + | |||
| + | |||
| + | >>> print (str.split( ))[0] | ||
| + | this | ||
| + | ===string replace=== | ||
| + | |||
| + | string = "geeks for geeks geeks geeks geeks" | ||
| + | |||
| + | Prints the string by replacing geeks by Geeks | ||
| + | print(string.replace("geeks", "Geeks")) | ||
| + | |||
| + | Prints the string by replacing only 3 occurrence of Geeks | ||
| + | print(string.replace("geeks", "GeeksforGeeks", 3)) | ||
| + | |||
| + | |||
| + | ===grep equivalent=== | ||
| + | use splitlines and test for string using regex via re.search | ||
| + | |||
| + | <source lang="python"> | ||
| + | import re | ||
| + | txt = "foo\nbar\n foo\n bar" | ||
| + | for line in txt.splitlines(): | ||
| + | if re.search("\sfoo", line): | ||
| + | print line | ||
| + | </source> | ||
| + | |||
| + | ==System-specific parameters and functions== | ||
| + | ===Command line arguments - sys.argv=== | ||
| + | required... | ||
| + | <br>import sys | ||
| + | <br>usage.... | ||
| + | <br>sys.argv[0] = name of script | ||
| + | <br>sys.argv[1] = first arg | ||
| + | <br>sys.argv[x] = xth arg, where x=some integer | ||
| + | <br>len(sys.argv) = number of args | ||
| + | <br> str(sys.argv) = argument list | ||
| + | |||
| + | [ https://medium.com/swlh/python-argparse-by-example-a530eb55ced9 Python Argparse by Example - Rupert Thomas] | ||
| + | |||
| + | [https://docs.python.org/3/library/argparse.html https://docs.python.org/3/library/argparse.html] | ||
| + | |||
| + | ===accessing input from a pipe=== | ||
| + | script that takes input from pipe and outputs it again to stdout | ||
| + | |||
| + | <source lang="python"> | ||
| + | import sys | ||
| + | |||
| + | for line in iter(sys.stdin.readline, ''): | ||
| + | sys.stdout.write(line) | ||
| + | </source> | ||
Latest revision as of 13:34, 14 July 2022
Contents |
Introduction
Lexical analysis
Data model
Execution model
Expressions
Simple statements
variable operations
assigenment examples
simple string assignment
>>> var1 = 'foo'
this automatically creates a variable of type string
>>> type(var1) <type 'str'>
printing your variable...
>>> print var1 foo
string assignment like above must be incapsulated by quotes or the right side is interpretted as a variable name.
example:
>>> var1 = foo Traceback (most recent call last): File "<stdin>", line 1, in ? NameError: name 'foo' is not defined
integer variable
>>> my_int_var1 = 1 >>> print my_int_var1 1
assigning a variable to another variable
>>> var2 = 'bar' >>> var1 = var2 >>> print var1 bar
muli-variable example:
>>> var1 = 'foo' >>> var2 = 'bar' >>> new_var = "%s %s" % (var1,var2) >>> print new_var foo bar
print sing variable named foo
>>> print foo
print variables with text
print 'my variable is %s' % FOO
or
print 'my variable are %s %s' % (FOO, BAR)
print without a newline, use comma at the end of the print statement
for i in range(10): ... print i, ... else: ... print ... 0 1 2 3 4 5 6 7 8 9
Common string operations
print nth word of string
print s.split()[n]
str = "this is string example....wow!!!" print (str.split( )) print (str.split('i',1)) print (str.split('w'))
>>> print (str.split( ))[0] this
string replace
string = "geeks for geeks geeks geeks geeks"
Prints the string by replacing geeks by Geeks
print(string.replace("geeks", "Geeks"))
Prints the string by replacing only 3 occurrence of Geeks
print(string.replace("geeks", "GeeksforGeeks", 3))
grep equivalent
use splitlines and test for string using regex via re.search
import re txt = "foo\nbar\n foo\n bar" for line in txt.splitlines(): if re.search("\sfoo", line): print line
System-specific parameters and functions
Command line arguments - sys.argv
required...
import sys
usage....
sys.argv[0] = name of script
sys.argv[1] = first arg
sys.argv[x] = xth arg, where x=some integer
len(sys.argv) = number of args
str(sys.argv) = argument list
[ https://medium.com/swlh/python-argparse-by-example-a530eb55ced9 Python Argparse by Example - Rupert Thomas]
https://docs.python.org/3/library/argparse.html
accessing input from a pipe
script that takes input from pipe and outputs it again to stdout
import sys for line in iter(sys.stdin.readline, ''): sys.stdout.write(line)
